Clean up OUTPUT_IS_SRGB redefinitions

drivers/gles3/storage/material_storage.cpp

@@ -1619,7 +1619,6 @@ MaterialStorage::MaterialStorage() {
 		actions.renames["INSTANCE_CUSTOM"] = "instance_custom";
 		actions.renames["SCREEN_UV"] = "screen_uv";
 		actions.renames["DEPTH"] = "gl_FragDepth";
-		actions.renames["OUTPUT_IS_SRGB"] = "true";
 		actions.renames["FOG"] = "fog";
 		actions.renames["RADIANCE"] = "custom_radiance";
 		actions.renames["IRRADIANCE"] = "custom_irradiance";

servers/rendering/renderer_rd/forward_clustered/scene_shader_forward_clustered.cpp

@@ -616,7 +616,6 @@ void SceneShaderForwardClustered::init(const String p_defines) {
 		actions.renames["INSTANCE_CUSTOM"] = "instance_custom";
 		actions.renames["SCREEN_UV"] = "screen_uv";
 		actions.renames["DEPTH"] = "gl_FragDepth";
-		actions.renames["OUTPUT_IS_SRGB"] = "true";
 		actions.renames["FOG"] = "fog";
 		actions.renames["RADIANCE"] = "custom_radiance";
 		actions.renames["IRRADIANCE"] = "custom_irradiance";

servers/rendering/renderer_rd/forward_mobile/scene_shader_forward_mobile.cpp

@@ -496,7 +496,6 @@ void SceneShaderForwardMobile::init(const String p_defines) {
 		actions.renames["INSTANCE_CUSTOM"] = "instance_custom";
 		actions.renames["SCREEN_UV"] = "screen_uv";
 		actions.renames["DEPTH"] = "gl_FragDepth";
-		actions.renames["OUTPUT_IS_SRGB"] = "true";
 		actions.renames["FOG"] = "fog";
 		actions.renames["RADIANCE"] = "custom_radiance";
 		actions.renames["IRRADIANCE"] = "custom_irradiance";