null: Get rid of some register type definitions.

These are no longer used.

Change-Id: Ic6a35e8a7e25eab9d21a3eef683914e01508c6d7
Reviewed-on: https://gem5-review.googlesource.com/c/14463
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

src/arch/null/registers.hh

@@ -47,10 +47,7 @@
 
 namespace NullISA {
 
-typedef RegVal IntReg;
-typedef RegVal FloatReg;
 typedef uint8_t CCReg;
-typedef RegVal MiscReg;
 const RegIndex ZeroReg = 0;
 
 // Not applicable to null