initdb required: GIN compare support function

Previously, the jsonb_ops GIN opclass followed the example of
gin_hstore_ops in using bttextcmp() as its support function 1.  This
makes a certain amount of sense, since the opclass storage format is
text in both cases.  However, there is no need to pay the additional
overhead of collation-aware comparisons, since the ordering of keys
serialized as text within a gin_jsonb_ops GIN B-Tree is merely an
implementation detail of no consequence to users.

In passing, perform a little diff minimization.