compiler.h: Remove caa_unqual_scalar_typeof

compiler.h: Remove caa_unqual_scalar_typeof

commit dd8987a4052e ("Revert "compiler.h: Introduce caa_unqual_scalar_typeof"")
removed caa_unqual_scalar_typeof because it uses _Generic, which
requires C11, but liburcu supports C99.

caa_unqual_scalar_typeof was re-introduced by commit d18544842bdf
("Add CMM memory model"), even though it is unused within liburcu.

Remove it again.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I7713504433d142aee1bb1a39492843cd73b37fc2