Remove URL-specific pre-validation from xprofile_set_field_data()

This validation is intended to catch URL submissions that do not have a scheme
(http://) attached, and to add it preemptively. However, we want to add this
validation in a more centralized location than here.

See #5501

git-svn-id: https://buddypress.svn.wordpress.org/trunk@8670 cdf35c40-ae34-48e0-9cc9-0c9da1808c22