Updated runtime files. Remove version checks for Vim older than 6.0.

runtime/syntax/lex.vim

@@ -8,11 +8,8 @@
 " Option:
 "   lex_uses_cpp : if this variable exists, then C++ is loaded rather than C
 
-" For version 5.x: Clear all syntax items
-" For version 6.x: Quit when a syntax file was already loaded
-if version < 600
-  syntax clear
-elseif exists("b:current_syntax")
+" quit when a syntax file was already loaded
+if exists("b:current_syntax")
   finish
 endif