Remove some unnecessary uses of nub_break_t in the arm specific
support files for debugserver to fix a build failure for arm.  Also
remove some of the code used for software-driven single instruction
stepping; this is slowly being yanked out and these particular bits
overlap with the nub_break_t going away.



git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@184828 91177308-0d34-0410-b5e6-96231b3b80d8