Update Xcode.gitignore

- Remove a reminder to look at files that don't exist anymore
- Remove ignore rules for an IDE from 2007
- Remove an ignore rule for Gcc which is no longer used since 2013

Global/Xcode.gitignore

-# Xcode
-#
-# gitignore contributors: remember to update Global/Xcode.gitignore, Objective-C.gitignore & Swift.gitignore
-
 ## User settings
 xcuserdata/
 
-## compatibility with Xcode 8 and earlier (ignoring not required starting Xcode 9)
+## Xcode 8 and earlier
 *.xcscmblueprint
 *.xccheckout
-
-## compatibility with Xcode 3 and earlier (ignoring not required starting Xcode 4)
-build/
-DerivedData/
-*.moved-aside
-*.pbxuser
-!default.pbxuser
-*.mode1v3
-!default.mode1v3
-*.mode2v3
-!default.mode2v3
-*.perspectivev3
-!default.perspectivev3
-
-## Gcc Patch
-/*.gcno