cmd/internal/obj/x86: remove ctxt.Curp references
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 <cdc248cc4d32e4fbfe04e45228163bcecd48a0b9@gmail.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Keith Randall <8c99c3a9284e493be632950b84cd789d08ed3e9d@golang.org>

Cofyc/go,golang/go,vsekhar/elastic-go,codestation/go,ImJasonH/go,golang/go,golang/go,cloudflare/go,Cofyc/go,nawawi/go,cloudflare/go,CAFxX/go,codestation/go,akutz/go,cloudflare/go,vsekhar/elastic-go,josharian/go,cloudflare/go,polyverse-security/go,josharian/go,CAFxX/go,codestation/go,cloudflare/go,akutz/go,akutz/go,vsekhar/elastic-go,cloudflare/go,golang/go,codestation/go,akutz/go,christopher-henderson/Go,derekmarcotte/go,CAFxX/go,nawawi/go,CAFxX/go,Cofyc/go,codestation/go,polyverse-security/go,CAFxX/go,ImJasonH/go,Cofyc/go,linux-on-ibm-z/go,derekmarcotte/go,nawawi/go,CAFxX/go,nawawi/go,codestation/go,ImJasonH/go,nawawi/go,akutz/go,linux-on-ibm-z/go,nawawi/go,linux-on-ibm-z/go,josharian/go,nawawi/go,derekmarcotte/go,golang/go,josharian/go,golang/go,derekmarcotte/go,ImJasonH/go,linux-on-ibm-z/go,ImJasonH/go,Cofyc/go,nawawi/go,linux-on-ibm-z/go,derekmarcotte/go,golang/go,linux-on-ibm-z/go,cloudflare/go,CAFxX/go,polyverse-security/go,CAFxX/go,linux-on-ibm-z/go,vsekhar/elastic-go,akutz/go,polyverse-security/go,cloudflare/go,golang/go,derekmarcotte/go,ImJasonH/go,linux-on-ibm-z/go,derekmarcotte/go,josharian/go,josharian/go,codestation/go,akutz/go,Cofyc/go,vsekhar/elastic-go,ImJasonH/go,Cofyc/go,Cofyc/go,ImJasonH/go,polyverse-security/go,josharian/go,vsekhar/elastic-go,akutz/go,vsekhar/elastic-go,vsekhar/elastic-go,codestation/go,derekmarcotte/go,polyverse-security/go,polyverse-security/go,polyverse-security/go,josharian/go