Remove the dynamic-docstring-function feature.

Remove the dynamic-docstring-function feature.

* emacs-lisp/advice.el (ad--make-advised-docstring): Change args.
Ignore function-documentation property when getting documentation.
(ad-activate-advised-definition): Use function-documentation
generate the docstring.
(ad-make-advised-definition): Don't call
ad-make-advised-definition-docstring.
(ad-make-advised-definition-docstring, ad-advised-definition-p):
Delete functions.

* emacs-lisp/nadvice.el (advice--make-docstring): Change args.
(advice--docstring): Delete variable.
(advice--make-1): Leave the docstring empty.
(advice-add): Use function-documentation for advised docstring.

* progmodes/sql.el (sql-help): Use function-documentation instead
of dynamic-docstring-function property.  No need to autoload now.
(sql--help-docstring): New variable.
(sql--make-help-docstring): Use it.

* doc.c (Fdocumentation): Remove dynamic-docstring-function.