[sanitizer_common] Remove hacks for __builtin_return_address abuse on SPARC

As detailed in Issue #57624, the introduction of
`__builtin_extract_return_address` to `GET_CALLER_PC` in
4248f32b
<https://reviews.llvm.org/rG4248f32b9ebe87c7af8ee53911efd47c2652f488> broke
`TestCases/Misc/missing_return.cpp` on Solaris/SPARC.  Unlike most other
targets, the builtin isn't a no-op on SPARC and thus has always been
necessary. Its lack had previously been worked around by calls to
`GetNextInstructionPc` in `sanitizer_stacktrace_sparc.cpp`
(`BufferedStackTrace::UnwindFast`) and `sanitizer_unwind_linux_libcdep.cpp`
(`BufferedStackTrace::UnwindSlow`).  However, those calls are superfluous
now and actually harmful.

This patch removes those hacks, fixing the failure.

Tested on `sparcv9-sun-solaris2.11` and on `sparc-sun-solaris2.11` in the
GCC tree.  On the latter, several more testcase failures had been caused by
this issue since ASan actually works with `gcc` on SPARC, unlike `clang`.

Differential Revision: https://reviews.llvm.org/D156504