Remove xmm_r_r inst data structure and cases after related refactoring

Removes unneeded data structure that was holding instructions for
xmm based move instructions. These instructions can should be categorized
as rm not just r. This change is intended to simplify organization and
cases when lowering.

cranelift/codegen/src/isa/x64/inst/emit.rs

@@ -1025,32 +1025,6 @@ pub(crate) fn emit(inst: &Inst, sink: &mut MachBuffer<Inst>) {
             }
         }
 
-        Inst::XMM_R_R { op, src, dst } => {
-            let opcode = match op {
-                SseOpcode::Movss => 0x0F10,
-                SseOpcode::Movsd => 0x0F10,
-                SseOpcode::Movd => 0x0F6E,
-                _ => unimplemented!("XMM_R_R opcode"),
-            };
-
-            let prefix = match op {
-                SseOpcode::Movss => LegacyPrefix::_F3,
-                SseOpcode::Movsd => LegacyPrefix::_F2,
-                SseOpcode::Movd => LegacyPrefix::_66,
-                _ => unimplemented!("XMM_R_R opcode"),
-            };
-
-            emit_std_reg_reg(
-                sink,
-                prefix,
-                opcode,
-                2,
-                dst.to_reg(),
-                *src,
-                RexFlags::clear_w(),
-            );
-        }
-
         Inst::XMM_MOV_RM_R {
             op,
             src: src_e,