sh: oprofile: Kill off bitrotted SH7750 driver.

This kills off the old SH7750 oprofile driver, preferring perf instead.
As this driver has a number of bugs that no one seems to have noticed,
it's safe to kill this off now rather than providing an extended
transition period.

The old oprofile framework is still kept in place for now, primarily to
give out-of-tree drivers a chance to transition off. But this too will be
killed off in short order.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>