Remove ClassMemberDeclaration props: isNative/isSynchronized/isStrictFP

Summary:
Also remove left-over bits for final property

All added in 816bf9de8b91314965de27fb5e855eb0d7486871 "to allow java
features to be used (without subclassing of major generic classes)".
But given kdevjava unported to qt5 & unmaintained for years and
nothing else using these properties (by what lxr.kde.org showed),
removing them helps keeping the code clean and as simple as possible.

Reviewers: KDevelop, egospodinova, ematirov, brauch, kfunk

Reviewed By: KDevelop, brauch, kfunk

Subscribers: brauch, kdevelop-devel

Differential Revision: https://phabricator.kde.org/D7098