[PowerPC] Remove non-existent operand of CP_COPY instruction (#153867)

The operand is not encoded, decoded, or printed and would break MCInst
verification if we had one.
Extracted from #156358, where the extra operand causes DecoderEmitter
to emit an error about an operand with a missing encoding.

Author: s-barannikov

llvm/lib/Target/PowerPC/PPCInstr64Bit.td

@@ -1984,7 +1984,7 @@ def : Pat<(int_ppc_darnraw), (DARN 2)>;
 
 class X_RA5_RB5<bits<6> opcode, bits<10> xo, string opc, RegisterOperand ty,
                    InstrItinClass itin, list<dag> pattern>
-  : X_L1_RS5_RS5<opcode, xo, (outs), (ins ty:$RA, ty:$RB, u1imm:$L),
+  : X_L1_RS5_RS5<opcode, xo, (outs), (ins ty:$RA, ty:$RB),
                  !strconcat(opc, " $RA, $RB"), itin, pattern>{
    let L = 1;
 }