Stop requiring an explicit return from perl subroutines

The consensus of the project appears to be that this provides little
benefit and is simply an annoyance.

Discussion: https://postgr.es/m/27481.1586618092@sss.pgh.pa.us

src/tools/perlcheck/perlcriticrc

@@ -22,7 +22,3 @@ verbose = %f: %m at line %l, column %c.  %e.  ([%p] Severity: %s)\n
 # insist on use of the warnings pragma
 [TestingAndDebugging::RequireUseWarnings]
 severity = 5
-
-# for now raise severity of this to level 5
-[Subroutines::RequireFinalReturn]
-severity = 5