Remove ShaderGraph submodule

.gitmodules

 	path = PostProcessing
 	url = https://github.com/Unity-Technologies/PostProcessing
 	branch = v2
-[submodule "ShaderGraph"]
-	path = ShaderGraph
-	url = https://github.com/Unity-Technologies/ShaderGraph
 [submodule "Tests/UTF_Core"]
 	path = Tests/UTF_Core
 	url = https://github.com/Unity-Technologies/UTF_Core.git

ShaderGraph.meta

-fileFormatVersion: 2
-guid: c4d536ecfc4cf3c4999d7a81e2d718e6
-folderAsset: yes
-DefaultImporter:
-  externalObjects: {}
-  userData: 
-  assetBundleName: 
-  assetBundleVariant: