Use API function rather than direct SQL query in bp_xprofile_filter_user_query_populate_extras()

Using BP_XProfile_ProfileData::get_value_byid() means cutting down on our
overall number of direct SQL queries, and has the additional benefit of
inheriting the object caching implemented there.

git-svn-id: https://buddypress.svn.wordpress.org/trunk@7810 cdf35c40-ae34-48e0-9cc9-0c9da1808c22