webserver/build-webserver-image: Don't use php symlink

make-container-image/webserver/build-webserver-image:

Don't try to include any php-* directory from
/srv/mediawiki-staging. The changes made for T359643 have removed
the need for this. The webserver image has been working fine for
the last 3 weeks or so with a dangling php symlink.

Also, exclude /srv/mediawiki-staging/scap from the rsync.

make-container-image/support/build-image-incr.py:
Updated to handle unsupplied --exclude or --include options.

Bug: T359643