Repository*: no need to register libraries built via ExternalProject

Only libraries (and similar for executables) built as Library need to be
registered; those built via ExternalProject are delivered by Project and
used via gb_LinkTarget_add_libs.  This also means there is no need to
mangle the names in RepositoryFixes.mk.

Change-Id: Ib0b67f54e2eb6efdb0c454c9e2dd599ada229676
Reviewed-on: https://gerrit.libreoffice.org/6533
Tested-by: LibreOffice gerrit bot <gerrit@libreoffice.org>
Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>
Tested-by: Markus Mohrhard <markus.mohrhard@googlemail.com>