games-engines/openxcom: remove obsolete patch from live

Feel like this package could use more attention / new snapshot
(haven't really looked), but at least dropping this obsolete patch.

Closes: https://bugs.gentoo.org/865417
Signed-off-by: Ionen Wolkens <ionen@gentoo.org>

games-engines/openxcom/files/openxcom-9999-mandir.patch

@@ -1,9 +0,0 @@
---- a/docs/CMakeLists.txt	2021-02-27 13:15:37.168240019 +0100
-+++ b/docs/CMakeLists.txt	2021-02-27 13:16:28.640486232 +0100
-@@ -38,5 +38,5 @@
- 
- # Only useful for make install/package under *nix OSes, but not macOS.
- if ( UNIX AND NOT APPLE )
--    INSTALL(FILES ${CMAKE_CURRENT_SOURCE_DIR}/openxcom.6 DESTINATION ${CMAKE_INSTALL_PREFIX}/man/man6)
-+    INSTALL(FILES ${CMAKE_CURRENT_SOURCE_DIR}/openxcom.6 DESTINATION ${CMAKE_INSTALL_PREFIX}/share/man/man6)
- endif ()

games-engines/openxcom/openxcom-9999.ebuild

@@ -1,4 +1,4 @@
-# Copyright 1999-2021 Gentoo Authors
+# Copyright 1999-2022 Gentoo Authors
 # Distributed under the terms of the GNU General Public License v2
 
 EAPI=7
@@ -33,8 +33,6 @@ BDEPEND="doc? ( app-doc/doxygen )"
 
 DOCS=( README.md )
 
-PATCHES=( "${FILESDIR}/${P}-mandir.patch" ) # TODO: GNUInstallDirs
-
 src_compile() {
 	cmake_src_compile
 	use doc && cmake_build doxygen