Remove the SH atomic implementation...

Remove the SH atomic implementation...

... but keep SH-4a, which provides a more efficient implementation. The
implementation removed here was very similar to the code removed by
commit dc5388e79b71d796c1207681235cf007c39810bd.

Support for SH can be provided by qatomic_gcc.h, or re-added in the
future if absolutely necessary.

Change-Id: Ic38b57c9513fc9c3c99ba7e102780a3939b735b9
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>