Update Objective-C and Swift to match Xcode.gitignore

The Objective-C and Swift gitignore files are missing *.xccheckout
and *.xcscmblueprint, but these are still included in the Xcode
gitignore. This commit synchronises the three files.

The files themselves contain information about the user's local
source control status and shouldn't be included in most Xcode
repositories.

*.xcuserstate appears to always be contained in xcuserdata/
which is already ignored.