mon: Modified an if statement to check if there were maps to trim

mon: Modified  an if statement to check if there were maps to trim

When to_remove is 0 and first commited is 0 the maybe trim function
in paxos service.cc calls the trim function with argument to and from
having the  same value, which causes the assert statement in the trim
function to fail and the monitor to crash. Modifying the if statement
trim_to <= first commited checks this condition before calling the trim
function and returns if true

Fixes: https://tracker.ceph.com/issues/71610
Signed-off-by: Shreya Subramanian <Shreya.Subramanian@ibm.com>