cmd/compile: remove {Mark,Pop}dcl calls in bimport
cmd/compile: remove {Mark,Pop}dcl calls in bimport

These were previously only relevant for recording scoping level so
that invalid 'fallthrough' statements could be rejected. However,
that's handled differently since CL 61130 (in particular, there's no
use of types.Block anymore), so these calls can be safely removed.

Passes toolstash-check.

Change-Id: I8631b156594df85b8d39f57acad3ebcf099d52f9
Reviewed-on: https://go-review.googlesource.com/64810
Run-TryBot: Matthew Dempsky <e56ac2c500064424afac424d4b5e53bd0570a731@google.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Robert Griesemer <a6752097faebf1f02d80107d77a9be009089afe3@golang.org>

cloudflare/go,golang/go,josharian/go,codestation/go,cloudflare/go,polyverse-security/go,polyverse-security/go,cloudflare/go,CAFxX/go,CAFxX/go,akutz/go,akutz/go,Cofyc/go,josharian/go,golang/go,CAFxX/go,codestation/go,cloudflare/go,josharian/go,CAFxX/go,polyverse-security/go,Cofyc/go,golang/go,nawawi/go,golang/go,golang/go,codestation/go,cloudflare/go,polyverse-security/go,codestation/go,Cofyc/go,akutz/go,CAFxX/go,polyverse-security/go,josharian/go,josharian/go,Cofyc/go,josharian/go,akutz/go,nawawi/go,nawawi/go,josharian/go,codestation/go,christopher-henderson/Go,nawawi/go,polyverse-security/go,golang/go,akutz/go,akutz/go,akutz/go,Cofyc/go,Cofyc/go,CAFxX/go,codestation/go,nawawi/go,cloudflare/go,akutz/go,cloudflare/go,nawawi/go,codestation/go,josharian/go,Cofyc/go,nawawi/go,cloudflare/go,polyverse-security/go,CAFxX/go,codestation/go,Cofyc/go,nawawi/go,CAFxX/go,golang/go,golang/go,polyverse-security/go