Revert "Fix a race condition between "ephemeral watchpoint disable/enable" and...

Revert "Fix a race condition between "ephemeral watchpoint disable/enable" and continue in commands."

This reverts commit r284795, as it breaks watchpoint handling on arm (and
presumable all architectures that report watchpoint hits without executing the
tripping instruction).

There seems to be something fundamentally wrong with this patch: it uses
process_sp->AddPreResumeAction to re-enable the watchpoint, but the whole point
of the step-over-watchpoint logic (which AFAIK is the only user of this class) is
to disable the watchpoint *after* we resume to do the single step.

I have no idea how to fix this except by reverting the offending patch.

llvm-svn: 284817