glcpp: Remove 2 shift/reduce conflicts from the grammar.

Since we have productions to turn "defined FOO" and "defined ( FOO )"
into a conditional_token we don't need to list DEFINED as an operator
as well. Doing so just introduces the shift/reduce ambiguity with no
benefit.

src/glsl/glcpp/glcpp-parse.y

@@ -478,7 +478,6 @@ operator:
 |	','			{ $$ = ','; }
 |	'='			{ $$ = '='; }
 |	PASTE			{ $$ = PASTE; }
-|	DEFINED			{ $$ = DEFINED; }
 ;
 
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