cmd/internal/obj/x86: remove NOP that crept into framepointer fix

Followup to CL 7728.

Change-Id: Ibb0fed7816aab459a94720b139a7737fad65bea2
Reviewed-on: https://go-review.googlesource.com/8425Reviewed-by: Austin Clements <austin@google.com>

src/cmd/internal/obj/x86/asm6.go

@@ -2911,7 +2911,6 @@ var bpduff1 = []byte{
 }
 
 var bpduff2 = []byte{
-	0x90,
 	0x48, 0x8b, 0x6d, 0x00, // MOVQ 0(BP), BP
 }