posix-cpu-timers: Remove the odd field rename defines

The last users of the odd define based renaming of struct task_cputime
members are gone. Good riddance.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lkml.kernel.org/r/20190821192921.499058279@linutronix.de