cmd/compile: remove ErrorfVers and base.Flag.Lang hack

ErrorfVers used to be used by typecheck to report when new language
functionality was used, but the -lang flag (from go.mod) was set to an
older version. However, all of the callers have been since removed,
now that this is handled by types2.

And for the same reason, we can stop changing base.Flag.Lang. This was
previously a workaround so that the unified frontend could generate
arbitrary IR without upsetting typecheck, at a time when typecheck was
itself a real frontend. Now it's just a glorified desugaring pass.

Change-Id: I1c0316dbfe2e08ba089acd50fdfe20b17176be25
Reviewed-on: https://go-review.googlesource.com/c/go/+/522877
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Auto-Submit: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Keith Randall <khr@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

0 files changed, 0 insertions, 0 deletions