glsl2: Remove incorrect assertion in the parser.

This assertion is triggered by method calls (i.e. array.length()), where
subexpressions[1] is an ast_function_call expression.  Since the
assertion itself had a comment saying it could be removed eventually,
simply do so.

Causes negative glslparser tests array-length-110.frag,
array-length-args.frag, and array-length-unsized.frag to pass, but only
because the length() method is not supported yet.

src/glsl/glsl_parser.ypp

@@ -304,12 +304,6 @@ postfix_expression:
 	}
 	| function_call
 	{
-	   /* Function call parameters used to be stored as a circular list in
-	    * subexpressions[1].  They are now stored as a regular list in
-	    * expressions.  This assertion validates that the old code was
-	    * correctly converted.  It can eventually be removed.
-	    */
-	   assert($1->subexpressions[1] == NULL);
 	   $$ = $1;
 	}
 	| postfix_expression '.' IDENTIFIER