Since ae855bf48163ff64d94cfc34aff8e37abdb5518d and
35518c92365cc183ba6cce2a4d284a130c0ca13f the ridl,jurt und unoil jars
were merged into libreoffice.jar. Adapt the buck build correspondingly.

Preserve the publishing of merged jars for now with dummy content and
consider to remove them in future releases.

Test Plan:

1. To replace version number with upcoming release version:

  $ solenv/bin/version.py 7.1.0

2. To install the API to local Maven repository:

  $ VERBOSE=1 buck build api_install

3. To deploy the API to Maven Central:

  $ VERBOSE=1 buck build api_deploy

Change-Id: Id1b2135682ab962c901b944f3c26aeead9a4b19b
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/93724
Tested-by: Jenkins
Reviewed-by: Christian Lohmaier <lohmaier+LibreOffice@googlemail.com>