Staging: rtl8712: Remove function r8712_setptm_cmd and r8712_gettssi_cmd

The function r8712_setptm_cmd and r8712_gettssi_cmd are not used
anywhere in the kernel so remove them. Also, remove their function
prototypes.

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