powerpc: Remove the unneeded trigger of decrementer interrupt in decrementer_check_overflow

Previously in order to handle the edge sensitive decrementers,
we choose to set the decrementer to 1 to trigger a decrementer
interrupt when re-enabling interrupts. But with the rework of the
lazy EE, we would replay the decrementer interrupt when re-enabling
interrupts if a decrementer interrupt occurs with irq soft-disabled.
So there is no need to trigger a decrementer interrupt in this case
any more.

Signed-off-by: Kevin Hao <haokexin@gmail.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>