[aon_timer/rtl] Minor cleanup for D2
[aon_timer/rtl] Minor cleanup for D2

Add an assertion to confirm stability of wakeup signal (related to

Remove redundant flops for interrupt pulse creation (the pulse is now
created by prim_pulse_sync).

Signed-off-by: Tom Roberts <f3b1a53ee1cbeb35a47033dea932030093853292@lowrisc.org>

lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan