Before gbuild'ification, solenv/inc/target.mk carefully produced two variants of
each type rdb, a plain one from calling idlc w/o -C and a *_doc variant from
calling idlc w/ -C ("generate complete type information, including
documentation").  After gbuild'ification, solenv/gbuild/UnoApiTarget.mk
unconditionally only produced "complete" type rdbs from calling idlc w/ -C.

It is unclear to me whether the old *_doc variants had actually been used for
anything (what got packaged into installation sets apparently were the plain,
slim variants; and autodoc apparently does not need the *_doc variants, either,
as it produces UNOIDL documentation directly from .idl files).  It is also
unclear to me whether the gbuild switch to effectively package complete, fat
rdbs was deliberate or not.  (The only client-visible change I see is that low-
level C/C++ typereg_reader_getDocumentation could now report something.  The
reflective UNO services at com.sun.star.reflection would not offer access to the
documenation anyway, however.)

The benefit of no longer including documentation in the packaged type rdbs is
size; the URE types.rdb shrinks from 1.2 MiB to 819 KiB, and offapi.rdb shrinks
from 11 MiB to 6.5 MiB.

Change-Id: Ib278f74fc3b22169e00a09d778807f8cf58520c4