glsl: Remove unused include from glsl_symbol_table.h

Only function-defs use glsl_type so forward declare instead.
Compile-tested on my Ivy-bridge system.

IWYU also suggests removing #include <new>, and this compiles fine.
I'm not familiar enough with memory management in C/C++ that I feel
comfortable removing this. Insights would be appreciated.

Reviewed-by: Tom Stellard <thomas.stellard@amd.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Signed-off-by: Thomas Helland <thomashelland90@gmail.com>

src/glsl/glsl_symbol_table.h

@@ -32,9 +32,9 @@ extern "C" {
 #include "program/symbol_table.h"
 }
 #include "ir.h"
-#include "glsl_types.h"
 
 class symbol_table_entry;
+class glsl_type;
 
 /**
  * Facade class for _mesa_symbol_table