msm: clock: Clean-up auto-off ops

Now that the voltage scaling code has been pushed up into clock.c,
RCG and branch clock auto-off ops do the same thing as the disable
ops.  Remove the duplicated/unnecessary code. The RPM clock auto-off
function does nothing and can be removed, also.

Change-Id: I2a42edc52b73f5198b1b81d053cf7d4775cf1a49
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>