Multiple modules: Remove all errors related to using 'madlib' as schema

Multiple modules used 'madlib' as a hardcoded schema name instead
of the generic MADLIB_SCHEMA that would be translated to the actual
schema where madlib is installed. This caused problems in
install-check and others tests. This has been rectified across the
product in this commit.
PLDA: Remove old code from methods

New LDA code replaces the old PLDA while eliminating all the memory
issues that the old code had. At this point, we can safely remove
the old code for the next release.
LDA: Fix a problem with PostgreSQL