perlapi: Fix up SV handling pod

perlapi: Fix up SV handling pod

The pod for this has gotten screwed up over the releases, with a section
entitled SV-Body Allocation containing a bunch of SV manipulation
functions, and another section with that name containing still more with
no real rhyme or reason as to why one would be in one vs the other.  And
one function was in both places.  This commit consolidates all these
into one section entitled "SV Manipulation Functions"