Bug 23113: members/pay.tt account_grp is not longer used

Bug 23113: members/pay.tt account_grp is not longer used

This patch removes obsolete markup from pay.tt.

To test, apply the patch and search the Koha codebase for instances of
"account_grp" There should be none.

Log in to the staff client and go to the account of a patron who has
fines. Confirm that the "Accounting" page ("Make a payment" tab) works
correctly.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>