[TSan] Remove unused setjmp definitions

The __interceptor_*setjmp() definitions appear to have been defined for
the purpose of TSAN_INTERCEPT(), but on non-Mac systems, it seems
TSAN_INTERCEPT() isn't even being used anymore for setjmp.

Remove them. Nothing should call them anyway (due to CHECK-fail), so
having the linker fail is better than failing at runtime.

Reviewed By: dvyukov

Differential Revision: https://reviews.llvm.org/D151218