lib/shadow/group/sgetgrent.c: Move free(3) call outside of helper

[alejandro-colomar]

This is for consistency with how this is done in
sgetsgent().

Now we need to make sure that the list is NULL before
the first call, which means that the 'grent' structure must
be cleared.  Since it's a static object, it's already true, but
let's be explicit about it.

Since we remember the address of the list in
grent.gr_mem (which is static), we don't need to keep
'members' being static too, so we get rid of one static
thing.

This removes a static variable.

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• This is a subset of ls #1272 at v3c.

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Revisions:

v1b

• Rebase

$ git rd 
1:  93eb0220f = 1:  11c744777 lib/shadow/group/sgetgrent.c: Move free(3) call outside of helper

v1c

• Rebase

$ git rd 
1:  11c744777 = 1:  afd79dccd lib/shadow/group/sgetgrent.c: Move free(3) call outside of helper

[alejandro-colomar]

• @hallyn , I'm going to break ls #1272 into small PRs so that we can reason about the changes better.