Remove unhelpful tooltips

These buttons should be self-explanatory.

Change-Id: I3ae973f093430cb3c1c88284267cff005caf7bff
Reviewed-on: https://gerrit.libreoffice.org/12397
Reviewed-by: Samuel Mehrbrodt <s.mehrbrodt@gmail.com>
Tested-by: Samuel Mehrbrodt <s.mehrbrodt@gmail.com>