Remove SetResumeState from POSIXThread::RefreshStateAfterStop

With the removal of ProcessLinux in r240543 this code is used only on
FreeBSD. FreeBSD isn't affected by whichever issue originally prompted
the addition of SetResumeState, so just remove it.

As discussed on the mailing list (and mentioned in a FIXME comment)
it shouldn't be called there.

llvm-svn: 240550