Deprecate clean_url() in favor of esc_url() and esc_url_raw()

[nacin]

Though eliminating a straight alias doesn't make much of a difference, the less validation and sanitization functions we have, the less confused plugin authors are, which hopefully means they try to write more secure the code.

We should merge clean_url() into esc_url(), giving esc_url() a $_context argument. esc_url_raw() can then call esc_url() with a $_context of 'db'.

(In [13297]) Use esc_url() instead of clean_url(). See #12309

[13299]