Remove clutter.symbols

The Visual Studio build files have been updated to not use it, so we can
remove it from the repository.
test-utils: Skip tests if no DISPLAY is set

Instead of just bailing out when initializing the test suite, we can do
a much better job and skip all the tests. This means that the TAP driver
will work correctly instead of dying a horrible death, and we get a nice
report with a proper cause of the test skipping.
Updated Greek translation