Fix some warnings regarding unnecessary imports and accessing static methods

My Galileo eclipse was complaining about unneeded import statements and
how static methods have been accessed in Diff.java. There was also one method
call which could be removed because he had no sideeffects and the return value
was not used. I fixed this so that there are no warnings anymore.

Signed-off-by: Christian Halstrick <christian.halstrick@sap.com>
Change-Id: I48d7e01536aab1524140d72af574e3fd7149cd23