Don't run meta_value through esc_sql() in bp_blogs_update_blogmeta()

The necessary sanitization happens in $wpdb, and the esc_sql() re-adds slashes
that were removed by stripslashes(). Fixing this bug just in time to refactor
it out :)

See #4551

git-svn-id: https://buddypress.svn.wordpress.org/trunk@7868 cdf35c40-ae34-48e0-9cc9-0c9da1808c22