Remove superfluous X11_FOUND check

It is REQUIRED in this context, so we can assume X11 has been found.

unix/x0vncserver/CMakeLists.txt

   target_link_libraries(x0vncserver ${LIBSYSTEMD_LIBRARIES})
 endif()
 
-if(X11_FOUND AND X11_XTest_LIB)
+if(X11_XTest_LIB)
   add_definitions(-DHAVE_XTEST)
   target_link_libraries(x0vncserver ${X11_XTest_LIB})
 else()
   message(WARNING "No XTest extension.  x0vncserver will be view-only.")
 endif()
 
-if(X11_FOUND AND X11_Xdamage_LIB)
+if(X11_Xdamage_LIB)
   add_definitions(-DHAVE_XDAMAGE)
   target_link_libraries(x0vncserver ${X11_Xdamage_LIB})
 else()
   message(WARNING "No DAMAGE extension.  x0vncserver will have to use the slower polling method.")
 endif()
 
-if(X11_FOUND AND X11_Xfixes_LIB)
+if(X11_Xfixes_LIB)
   add_definitions(-DHAVE_XFIXES)
   target_link_libraries(x0vncserver ${X11_Xfixes_LIB})
 else()
   message(WARNING "No XFIXES extension.  x0vncserver will not be able to show cursors.")
 endif()
 
-if(X11_FOUND AND X11_Xrandr_LIB)
+if(X11_Xrandr_LIB)
   add_definitions(-DHAVE_XRANDR)
   target_link_libraries(x0vncserver ${X11_Xrandr_LIB})
 else()