glsl: Remove unused include from hir_field_selection.cpp

Found with IWYU. Compile-tested on my Ivy-bridge system

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/hir_field_selection.cpp

@@ -22,7 +22,6 @@
  */
 
 #include "ir.h"
-#include "program/symbol_table.h"
 #include "glsl_parser_extras.h"
 #include "ast.h"
 #include "glsl_types.h"