pgsql: Get rid of bogus separate pg_proc entries for json_extract_path

Get rid of bogus separate pg_proc entries for json_extract_path operators.

These should not have existed to begin with, but there was apparently some
misunderstanding of the purpose of the opr_sanity regression test item
that checks for operator implementation functions with their own comments.
The idea there is to check for unintentional violations of the rule that
operator implementation functions shouldn't be documented separately
.... but for these functions, that is in fact what we want, since the
variadic option is useful and not accessible via the operator syntax.
Get rid of the extra pg_proc entries and fix the regression test and
documentation to be explicit about what we're doing here.

Branch
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REL9_4_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/c3096d57c8faa24aa5ff4cc7e87d989ce42ad05d

Modified Files
--------------
doc/src/sgml/func.sgml                   |    6 ++++--
src/include/catalog/catversion.h         |    2 +-
src/include/catalog/pg_operator.h        |    8 ++++----
src/include/catalog/pg_proc.h            |    4 ----
src/test/regress/expected/opr_sanity.out |   20 ++++++++++++--------
5 files changed, 21 insertions(+), 19 deletions(-)