Remove redundant SetLatch() calls in interrupt handling functions

Remove redundant SetLatch() calls in interrupt handling functions

Interrupt handling functions (e.g., HandleCatchupInterrupt(),
HandleParallelApplyMessageInterrupt()) are called only by
procsignal_sigusr1_handler(), which already calls SetLatch()
for the current process at the end of its processing.
Therefore, these interrupt handling functions do not need to
call SetLatch() themselves.

However, previously, some of these functions redundantly
called SetLatch(). This commit removes those unnecessary
calls.

While duplicate SetLatch() calls are redundant, they are
harmless, so this change is not backpatched.

Author: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Reviewed-by: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Reviewed-by: Fujii Masao <masao.fujii@gmail.com>
Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Reviewed-by: Dilip Kumar <dilipbalaut@gmail.com>
Discussion: https://postgr.es/m/CALj2ACWd5apddj6Cd885WwJ6LquYu_G81C4GoR4xSoDV1x-FEA@mail.gmail.com