Driver: Remove support for -fobjc-gc*

As a first step toward removing Objective-C garbage collection from
Clang, remove support from the driver.  I'm hoping this will flush out
any expected bots/configurations/whatever that might rely on it.

I've left the options behind temporarily in -cc1 to keep tests passing.
I'll kill them off entirely in a follow up when I've had a chance to
update/delete the rest of Clang.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@288872 91177308-0d34-0410-b5e6-96231b3b80d8