Strip down compiler messages to AspectJ-specific ones

Strip down compiler messages to AspectJ-specific ones

Delete all properties from messages_aspectj.properties which were just
copied from Eclipse and basically the same. This not only gets rid of
duplicates but also eliminates differences found between upstream and
AspectJ strings which were just cause by errors or oversights during
manual upgrade.

TODO:
  - Find a way to print the '-X' options as info instead of yielding
    'abort', making it seem as if compilation failed and print the usage
    message to stdErr instead of stdOut.
  - Eclipse also has misc.usage.warn, not just misc.usage, i.e. usage
    info specifically for warning options. Make sure that AspectJ uses
    it consistently.
  - Find a way to merge AspectJ-specific options into the standard
    Eclipse usage text instead of completely replacing it, further
    reducing the need to merge and copy upstream content.
Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>