staging: rtl8723bs: remove rtl8192c_rf.h

All functions declared in rtl8192c_rf.h have no definition/are not used
in any other file/anywhere. Checked with 'git grep <function_name>'.

Signed-off-by: Michael Straube <straube.linux@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>