cmd/internal/obj/x86: remove ctxt.Curp references

Empirically, p == ctxt.Curp here.
A scan of (the thousands of lines of) asm6.go
shows no clear opportunity for them to diverge.

Passes toolstash-check -all.

Updates #15756

Change-Id: I9f5ee9585a850fbe24be3b851d8fdc2c966c65ce
Reviewed-on: https://go-review.googlesource.com/38665
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

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

@@ -3029,7 +3029,7 @@ putrelv:
 
 		r := obj.Addrel(ctxt.Cursym)
 		*r = rel
-		r.Off = int32(ctxt.Curp.Pc + int64(asmbuf.Len()))
+		r.Off = int32(p.Pc + int64(asmbuf.Len()))
 	}
 
 	asmbuf.PutInt32(v)
@@ -3322,8 +3322,6 @@ func (asmbuf *AsmBuf) asmvex(ctxt *obj.Link, rm, v, r *obj.Addr, vex, opcode uin
 }
 
 func (asmbuf *AsmBuf) doasm(ctxt *obj.Link, p *obj.Prog) {
-	ctxt.Curp = p // TODO
-
 	o := opindex[p.As&obj.AMask]
 
 	if o == nil {