arch: Get rid of (some) unused VAddr types.

X86 actually defines and uses a VAddr bitunion, but the ARM, MIPS and
SPARC versions are just stubs and aren't used anywhere.

Change-Id: Iea8d0c8ab04ac1d95f49458f0fc41f291751da1a
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/33202
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>

src/arch/arm/pagetable.hh

@@ -49,12 +49,6 @@
 
 namespace ArmISA {
 
-struct VAddr
-{
-    VAddr(Addr a) { panic("not implemented yet."); }
-};
-
-
 // ITB/DTB page table entry
 struct PTE
 {

src/arch/mips/pagetable.hh

@@ -36,10 +36,6 @@
 
 namespace MipsISA {
 
-struct VAddr
-{
-};
-
 // ITB/DTB page table entry
 struct PTE
 {

src/arch/sparc/pagetable.hh

@@ -37,12 +37,8 @@
 
 class Checkpoint;
 
-namespace SparcISA {
-
-struct VAddr
+namespace SparcISA
 {
-    VAddr(Addr a) { panic("not implemented yet."); }
-};
 
 class TteTag
 {