Prune unused extra compiler modifiers.

ATM, the following are not used:

`org.eclipse.jdt.internal.compiler.lookup.ExtraCompilerModifiers.AccFromClassFile`
`org.eclipse.jdt.internal.compiler.lookup.ExtraCompilerModifiers.AccDefaultAbstract`

See that the latter relates to `https://github.com/eclipse-jdt/eclipse.jdt.core/issues/1600` - the overhaul/cleanup planned in overload methods resolution.

The following modifier `org.eclipse.jdt.internal.compiler.lookup.ExtraCompilerModifiers.AccImplicitlyDeclared` appears set only in some places - in particular the parser doesn't set it. This needs to be double checked.