Remove xproto and kbproto from pkg-config file

These are no longer needed for using the library, only building it. Most
users would still want xproto though, for the keysym definitions.

Signed-off-by: Ran Benita <ran234@gmail.com>

xkbcommon.pc.in

@@ -6,6 +6,5 @@ includedir=@includedir@
 Name: xkbcommon
 Description: XKB API common to servers and clients
 Version: @PACKAGE_VERSION@
-Requires: xproto kbproto >= 1.0.4
 Cflags: -I${includedir}
 Libs: -L${libdir} -lxkbcommon