Remove SQL_LANGUAGES, which was eliminated in SQL:2008, and
SQL_PACKAGES and SQL_SIZING_PROFILES, which were eliminated in
SQL:2011.  Since they were dropped by the SQL standard, the
information in them was no longer updated and therefore no longer
useful.

This also removes the feature-package association information in
sql_feature_packages.txt, but for the time begin we are keeping the
information which features are in the Core package (that is, mandatory
SQL features).  Maybe at some point someone wants to invent a way to
store that that does not involve using the "package" mechanism
anymore.

Discussion https://www.postgresql.org/message-id/flat/91334220-7900-071b-9327-0c6ecd012017%402ndquadrant.com