[DOCS] Remove outdated paragraph (#1582)

There is no necessity anymore for user functions to be prepended with `user_` anymore, so that confusing and vague sentence can be removed.

Co-authored-by: Johannes Nielsen <flykasual@gmail.com>

Author: github-actions[bot]

Documentation/Functions/Parsefunc.rst

@@ -190,9 +190,6 @@ userFunc
     Similar to, for example, :ref:`stdwrap-postUserFunc` in :ref:`stdWrap`,
     or :ref:`typolink.userFunc <typolink-userFunc>`.
 
-    Remember the function name must possibly be prepended :php:`user_`.
-
-
 ..  _parsefunc-nonTypoTagStdWrap:
 
 nonTypoTagStdWrap