util: Remove u_atomic.h's MSVC inline assembly.
util: Remove u_atomic.h's MSVC inline assembly.

There was already an intrinsics path that implemented all of the same
functions, plus more.

Reviewed-by: Jose Fonseca <61b5a29db2c0650f7c8510f93eece059c1b09320@vmware.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler