Commit df156a56c0 replaced "virtual"
by "override" where appropriate. Unfortunately, this had the
unintended consequence of producing numerous clang warnings. If
clang finds a override-modified function in a class definition,
it warns for *all* overriden virtual functions without the override
modifier.
To solve this, go the easy route and remove all overrides. At least
it is consistent.
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>