Don't try to install the manpage when using CMake

... there's no manpage on master

Fixup of aeebd86

Signed-off-by: Steffen Jaeckel <s@jaeckel.eu>

CMakeLists.txt

@@ -190,14 +190,6 @@ write_basic_package_version_file(
     COMPATIBILITY SameMajorVersion
 )
 
-# Windows uses a different help sytem.
-if((NOT WIN32) AND (NOT CMAKE_HOST_WIN32))
-# install manpage (not gzipped, some BSD's do not want it compressed?)
-install(FILES ${CMAKE_SOURCE_DIR}/doc/tommath.3
-        DESTINATION ${CMAKE_INSTALL_MANDIR}/man3/
-)
-endif()
-
 # install version file
 install(FILES ${PROJECT_VERSION_FILE}
         DESTINATION ${CONFIG_INSTALL_DIR}