Fix warnings about unused variables [-Wunused-variable]

Fixes the following GCC 5 warnings:
```
drivers/gles2/rasterizer_scene_gles2.cpp:1139:15: warning: unused variable 'offset' [-Wunused-variable]
drivers/gles2/rasterizer_scene_gles2.cpp:1205:39: warning: unused variable 'multi_mesh' [-Wunused-variable]
drivers/gles2/rasterizer_storage_gles2.cpp:359:7: warning: unused variable 'srgb' [-Wunused-variable]
drivers/gles2/shader_gles2.cpp:1016:45: warning: unused variable 'texture_hints' [-Wunused-variable]
editor/animation_track_editor.cpp:776:9: warning: unused variable 'keys_to' [-Wunused-variable]
editor/editor_inspector.cpp:273:7: warning: unused variable 'vs_height' [-Wunused-variable]
editor/editor_themes.cpp:202:10: warning: unused variable 'begin_time' [-Wunused-variable]
editor/editor_themes.cpp:239:10: warning: unused variable 'end_time' [-Wunused-variable]
editor/plugins/animation_blend_tree_editor_plugin.cpp:726:17: warning: unused variable 'an' [-Wunused-variable]
editor/plugins/script_text_editor.cpp:1278:8: warning: unused variable 'fold_state' [-Wunused-variable]
main/main.cpp:132:13: warning: 'use_vsync' defined but not used [-Wunused-variable]
modules/cvtt/image_compress_cvtt.cpp:231:8: warning: unused variable 'y_end' [-Wunused-variable]
modules/cvtt/image_compress_cvtt.cpp:311:6: warning: unused variable 'shift' [-Wunused-variable]
modules/gdscript/gdscript_editor.cpp:58:7: warning: unused variable 'th' [-Wunused-variable]
modules/gridmap/grid_map.cpp:1084:6: warning: unused variable 'ofs' [-Wunused-variable]
modules/theora/video_stream_theora.cpp:442:9: warning: unused variable 'tr' [-Wunused-variable]
modules/visual_script/visual_script_editor.cpp:2606:6: warning: unused variable 'count' [-Wunused-variable]
modules/visual_script/visual_script_editor.cpp:2829:6: warning: unused variable 'seq_count' [-Wunused-variable]
modules/visual_script/visual_script_editor.cpp:2844:24: warning: unused variable 'vnode_function' [-Wunused-variable]
modules/websocket/lws_peer.cpp:122:12: warning: unused variable 'peer_data' [-Wunused-variable]
modules/websocket/lws_peer.cpp:135:12: warning: unused variable 'peer_data' [-Wunused-variable]
modules/websocket/lws_peer.cpp:63:12: warning: unused variable 'peer_data' [-Wunused-variable]
modules/websocket/lws_peer.cpp:91:12: warning: unused variable 'peer_data' [-Wunused-variable]
platform/android/export/export.cpp:763:16: warning: unused variable 'node_size' [-Wunused-variable]
scene/gui/rich_text_label.cpp:850:10: warning: unused variable 'x_ofs' [-Wunused-variable]
scene/gui/text_edit.cpp:653:8: warning: unused variable 'tab_w' [-Wunused-variable]
scene/resources/bit_mask.cpp:186:6: warning: unused variable 'i' [-Wunused-variable]
scene/resources/mesh.cpp:549:20: warning: '_array_name' defined but not used [-Wunused-variable]
servers/audio/audio_rb_resampler.cpp:107:10: warning: unused variable 'v2' [-Wunused-variable]
servers/audio/audio_rb_resampler.cpp:108:10: warning: unused variable 'v3' [-Wunused-variable]
servers/audio/audio_rb_resampler.cpp:109:10: warning: unused variable 'v4' [-Wunused-variable]
servers/audio/audio_rb_resampler.cpp:110:10: warning: unused variable 'v5' [-Wunused-variable]
servers/audio/audio_rb_resampler.cpp:111:10: warning: unused variable 'v0n' [-Wunused-variable]
servers/audio/audio_rb_resampler.cpp:112:10: warning: unused variable 'v1n' [-Wunused-variable]
servers/audio/audio_rb_resampler.cpp:113:10: warning: unused variable 'v2n' [-Wunused-variable]
servers/audio/audio_rb_resampler.cpp:114:10: warning: unused variable 'v3n' [-Wunused-variable]
servers/audio/audio_rb_resampler.cpp:115:10: warning: unused variable 'v4n' [-Wunused-variable]
servers/audio/audio_rb_resampler.cpp:116:10: warning: unused variable 'v5n' [-Wunused-variable]
servers/visual/default_mouse_cursor.xpm:2:21: warning: 'default_mouse_cursor_xpm' defined but not used [-Wunused-variable]
```

1 files changed, 0 insertions, 3 deletions

diff --git a/modules/cvtt/image_compress_cvtt.cpp b/modules/cvtt/image_compress_cvtt.cpp
index 425d8db183..732b9cf733 100644
--- a/modules/cvtt/image_compress_cvtt.cpp
+++ b/modules/cvtt/image_compress_cvtt.cpp
@@ -228,8 +228,6 @@ void image_compress_cvtt(Image *p_image, float p_lossy_quality, Image::CompressS
 		uint8_t *out_bytes = &wb[dst_ofs];
 
 		for (int y_start = 0; y_start < h; y_start += 4) {
-			int y_end = y_start + 4;
-
 			CVTTCompressionRowTask row_task;
 			row_task.width = w;
 			row_task.height = h;
@@ -308,7 +306,6 @@ void image_decompress_cvtt(Image *p_image) {
 	int target_size = Image::get_image_data_size(w, h, target_format, p_image->has_mipmaps());
 	int mm_count = p_image->get_mipmap_count();
 	data.resize(target_size);
-	int shift = Image::get_format_pixel_rshift(target_format);
 
 	PoolVector<uint8_t>::Write wb = data.write();