Don't remove Register and Activate pages from `bp_core_get_directory_page_ids()`.

These two pages do not correspond to components, so they should be excluded
from `bp_is_active()` checks.

Props imath.
Fixes #6043.

git-svn-id: https://buddypress.svn.wordpress.org/trunk@9180 cdf35c40-ae34-48e0-9cc9-0c9da1808c22