Remove stale and unused (MC)TargetOptions comparators.

Summary:
I discovered accidentally that the operator== for TargetOptions
is stale - it is missing many fields that have been added over
the recent years. It isn't used, so remove it. Ditto for the
comparator in MCTargetOptions, which doesn't seem stale yet but is
unused.

Reviewers: echristo

Subscribers: llvm-commits, mehdi_amini

Differential Revision: https://reviews.llvm.org/D31301

llvm-svn: 298700