glsl2: Remove unnecessary use of 'struct' before type names

In C++ you don't have to say 'struct' or 'class' if the declaration of
the type has been seen.  Some compilers will complain if you use
'struct' when 'class' should have been used and vice versa.

Fixes bugzilla #29539.
diff --git a/src/glsl/ast_to_hir.cpp b/src/glsl/ast_to_hir.cpp
index 9d4448f..6e5d01e 100644
--- a/src/glsl/ast_to_hir.cpp
+++ b/src/glsl/ast_to_hir.cpp
@@ -986,7 +986,7 @@
 
       assert(operations[this->oper] == ir_binop_mod);
 
-      struct ir_rvalue *temp_rhs;
+      ir_rvalue *temp_rhs;
       temp_rhs = new(ctx) ir_expression(operations[this->oper], type,
 					op[0], op[1]);
 
@@ -1107,7 +1107,7 @@
 
       type = arithmetic_result_type(op[0], op[1], false, state, & loc);
 
-      struct ir_rvalue *temp_rhs;
+      ir_rvalue *temp_rhs;
       temp_rhs = new(ctx) ir_expression(operations[this->oper], type,
 					op[0], op[1]);
 
@@ -1131,7 +1131,7 @@
 
       type = arithmetic_result_type(op[0], op[1], false, state, & loc);
 
-      struct ir_rvalue *temp_rhs;
+      ir_rvalue *temp_rhs;
       temp_rhs = new(ctx) ir_expression(operations[this->oper], type,
 					op[0], op[1]);
 
@@ -1453,7 +1453,7 @@
 
 static void
 apply_type_qualifier_to_variable(const struct ast_type_qualifier *qual,
-				 struct ir_variable *var,
+				 ir_variable *var,
 				 struct _mesa_glsl_parse_state *state,
 				 YYLTYPE *loc)
 {
@@ -1620,7 +1620,7 @@
 
    foreach_list_typed (ast_declaration, decl, link, &this->declarations) {
       const struct glsl_type *var_type;
-      struct ir_variable *var;
+      ir_variable *var;
 
       /* FINISHME: Emit a warning if a variable declaration shadows a
        * FINISHME: declaration at a higher scope.