x11/xscreensaver: Adopt and clean up

Take maintainership as discussed with manu via email. Also clean up:

• Remove USES=desktop-file-utils again, the desktop files don't register any MIME types
• Add USES=shebangfix to fix the perl shebang, remove manual patching
• Remove MAKE_JOBS_UNSAFE, parallel builds seem to work just fine
• Format according to portclippy recommendations
• Update local patches

Approved by: x11 (manu)