Staging: rtl8723au: Remove unused macros

The macros PlatformAcquireSpinLock and PlatformReleaseSpinLock are
not used anywhere so remove them. Used grep to find occurences.

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>