Removed left and right brush arrows

- Removed left and right brush arrow indicators completely.
- Fixed bug when removing custom project brushes.

Assets/Graphics/left.png.import

@@ -1,34 +0,0 @@
-[remap]
-
-importer="texture"
-type="StreamTexture"
-path="res://.import/left.png-a0857f5581a7224bc4706f5b5b072c04.stex"
-metadata={
-"vram_texture": false
-}
-
-[deps]
-
-source_file="res://Assets/Graphics/left.png"
-dest_files=[ "res://.import/left.png-a0857f5581a7224bc4706f5b5b072c04.stex" ]
-
-[params]
-
-compress/mode=0
-compress/lossy_quality=0.7
-compress/hdr_mode=0
-compress/bptc_ldr=0
-compress/normal_map=0
-flags/repeat=0
-flags/filter=false
-flags/mipmaps=false
-flags/anisotropic=false
-flags/srgb=2
-process/fix_alpha_border=true
-process/premult_alpha=false
-process/HDR_as_SRGB=false
-process/invert_color=false
-stream=false
-size_limit=0
-detect_3d=true
-svg/scale=1.0

Assets/Graphics/right.png.import

@@ -1,34 +0,0 @@
-[remap]
-
-importer="texture"
-type="StreamTexture"
-path="res://.import/right.png-e081bdade321da1277a90c4dc43840cc.stex"
-metadata={
-"vram_texture": false
-}
-
-[deps]
-
-source_file="res://Assets/Graphics/right.png"
-dest_files=[ "res://.import/right.png-e081bdade321da1277a90c4dc43840cc.stex" ]
-
-[params]
-
-compress/mode=0
-compress/lossy_quality=0.7
-compress/hdr_mode=0
-compress/bptc_ldr=0
-compress/normal_map=0
-flags/repeat=0
-flags/filter=false
-flags/mipmaps=false
-flags/anisotropic=false
-flags/srgb=2
-process/fix_alpha_border=true
-process/premult_alpha=false
-process/HDR_as_SRGB=false
-process/invert_color=false
-stream=false
-size_limit=0
-detect_3d=true
-svg/scale=1.0