security/openvpn: drop man source patch

There has been a report of sporadic man-page rebuilds on OpenZFS.
While the patch order is correct, we do not intend to rebuild the
manpage (after a nobody -> openvpn change, for instance), and
we also patch the output files.  So just remove the source patch.

This should go without any functional changes, so ships without
bumping PORTREVISION.

There is an upstream ticket reporting a missing source file
in the tarball. https://community.openvpn.net/openvpn/ticket/1461

Reported by:    Jan Martin Mikkelsen
PR:             263116

security/openvpn/files/patch-doc_man-sections_generic-options.rst

---- doc/man-sections/generic-options.rst.orig	2021-10-31 16:17:17 UTC
-+++ doc/man-sections/generic-options.rst
-@@ -431,7 +431,7 @@ which mode OpenVPN is configured as.
-   able to gain control of an OpenVPN session. Though OpenVPN's security
-   features make this unlikely, it is provided as a second line of defense.
- 
--  By setting ``user`` to :code:`nobody` or somebody similarly unprivileged,
-+  By setting ``user`` to :code:`openvpn` or somebody similarly unprivileged,
-   the hostile party would be limited in what damage they could cause. Of
-   course once you take away privileges, you cannot return them to an
-   OpenVPN session. This means, for example, that if you want to reset an