Return true from Resolver::resolve() on success.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@192422 91177308-0d34-0410-b5e6-96231b3b80d8
Remove excessive allowRemainingUndefines() check.

allowRemainingUndefines() is already checked in Resolver::resolve(), so we
don't need to check it again after returning from it. It's actually not only
superfluous but buggy because a failure of resolve() does not always mean that
there is a remaining undefines.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@192423 91177308-0d34-0410-b5e6-96231b3b80d8