cmd/asm: drop legacy RETURN mnemonic on ppc64

Change-Id: I999b57ef5535c18e02cc27c9bc9f896d73126b50
Reviewed-on: https://go-review.googlesource.com/10674Reviewed-by: Russ Cox <rsc@golang.org>
Reviewed-by: Minux Ma <minux@golang.org>

src/cmd/asm/internal/arch/arch.go

@@ -351,7 +351,6 @@ func archPPC64() *Arch {
 	// Annoying aliases.
 	instructions["BR"] = ppc64.ABR
 	instructions["BL"] = ppc64.ABL
-	instructions["RETURN"] = ppc64.ARETURN
 
 	return &Arch{
 		LinkArch:       &ppc64.Linkppc64,

src/cmd/asm/internal/asm/testdata/ppc64.s

@@ -692,13 +692,13 @@ label1:
 //	}
 	NOP	$4
 
-// RETURN
+// RET
 //
 //	LRETRN	comma // asm doesn't support the trailing comma.
 //	{
 //		outcode(int($1), &nullgen, 0, &nullgen);
 //	}
-	RETURN
+	RET
 
 // END
 //

src/cmd/internal/obj/ppc64/9.out.go

@@ -535,5 +535,4 @@ const (
 	// aliases
 	ABR = obj.AJMP
 	ABL = obj.ACALL
-	ARETURN = obj.ARET
 )