Drop reference to non-existent C4XVER4

Version.txt was still adding C4XVER4 to the version string, which was
removed a while ago. This was mostly unproblematic though because
nothing besides the Windows game browser used this string.

Version.txt

@@ -47,12 +47,6 @@ set(C4ENGINEINFO        "${C4ENGINENAME}")
 
 set(C4VERSION           "${C4XVER1}.${C4XVER2}")
 
-if(C4XVER4 LESS 10)
-	set(C4VERSION       "${C4VERSION} [00${C4XVER4}]")
-elseif(C4XVERBUILD LESS 100)
-	set(C4VERSION       "${C4VERSION} [0${C4XVER4}]")
-else()
-	set(C4VERSION       "${C4VERSION} [${C4XVER4}]")
 endif()
 
 if(NOT ${C4VERSIONEXTRA} STREQUAL "")