glsl: Unify ir_constant::const_elements and ::components

There was no reason to treat array types and record types differently.
Unifying them saves a bunch of code and saves a few bytes in every
ir_constant.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Reviewed-by: Elie Tournier <elie.tournier@collabora.com>

src/compiler/glsl/ir.h

@@ -2262,12 +2262,9 @@ public:
     */
    union ir_constant_data value;
 
-   /* Array elements */
+   /* Array elements and structure fields */
    ir_constant **const_elements;
 
-   /* Structure fields */
-   exec_list components;
-
 private:
    /**
     * Parameterless constructor only used by the clone method