polkit-gnome: remove unrecognized configure options

Fix QA warning:
WARNING: QA Issue: polkit-gnome: configure was passed unrecognised options:
--disable-examples --disable-introspection [unknown-configure-option]

Signed-off-by: Yi Zhao <yi.zhao@windriver.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>