Get rid of empty IrBase class.

It isn't useful in any way now that the GC is out of the
picture, and the existance of a "dummy" toChars() method is
annoying when debugging.

ir/ir.h

@@ -23,11 +23,6 @@
 struct IRState;
 struct IrFunction;
 
-struct IrBase : Object
-{
-    virtual ~IrBase() {}
-};
-
 class Ir
 {
 public:

ir/irfunction.h

@@ -89,7 +89,7 @@ private:
 };
 
 // represents a function
-struct IrFunction : IrBase
+struct IrFunction
 {
     // constructor
     IrFunction(FuncDeclaration* fd);

ir/irfuncty.h

@@ -37,7 +37,7 @@ namespace llvm {
 
 // represents a function type argument
 // both explicit and implicit as well as return values
-struct IrFuncTyArg : IrBase
+struct IrFuncTyArg
 {
     /** This is the original D type as the frontend knows it
      *  May NOT be rewritten!!! */
@@ -85,7 +85,7 @@ struct IrFuncTyArg : IrBase
 };
 
 // represents a function type
-struct IrFuncTy : IrBase
+struct IrFuncTy
 {
     // return value
     IrFuncTyArg* ret;

ir/irmodule.h

@@ -19,7 +19,7 @@
 
 struct Module;
 
-struct IrModule : IrBase
+struct IrModule
 {
     IrModule(Module* module, const char* srcfilename);
     virtual ~IrModule();

ir/irstruct.h

@@ -26,7 +26,7 @@ struct StructInitializer;
 
 // represents a struct or class
 // it is used during codegen to hold all the vital info we need
-struct IrStruct : IrBase
+struct IrStruct
 {
     /// Constructor.
     IrStruct(AggregateDeclaration* agg);

ir/irvar.h

@@ -24,7 +24,7 @@
 
 struct IrFuncTyArg;
 
-struct IrVar : IrBase
+struct IrVar
 {
     IrVar(VarDeclaration* var);