Revert of #2988. TextMesh Pro files are not auto managed (#3134)

Unlike other packages, TextMesh Pro is not entirely managed by Unity's new Package Manager, and still imports some assets directly into the project.

Unity.gitignore

@@ -16,9 +16,6 @@
 # Uncomment this line if you wish to ignore the asset store tools plugin
 # /[Aa]ssets/AssetStoreTools*
 
-# TextMesh Pro files
-[Aa]ssets/TextMesh*Pro/
-
 # Autogenerated Jetbrains Rider plugin
 [Aa]ssets/Plugins/Editor/JetBrains*