[ob] Eliminate never-defined macros

[Andrew Cagney]

> Andrew Cagney <ac131313@redhat.com> writes:
> 
>> Neither MPW nor IS_TRAPPED_INTERNALVAR are defined in GDB.  Thiz zapps
>> the #ifdef code/comments that refered to them.
> 
> 
> Isn't MPW something #defined by the Macintosh Programmer's Workbench
> toolchain, like __GCC__?
> 
> (Not that it shouldn't be removed as obsolete; I just suspect the the
> rationale is wrong.)

#define MPW was removed with:

*** Changes in GDB 5.2:
* REMOVED configurations and files
Apple Macintosh (MPW) host and target           N/A host, powerpc-*-macos*


Andrew