go/types: update flag documentation for gotype command
go/types: update flag documentation for gotype command

The documentation refers to a non longer existing flag (-seq).
Remove those references.

Change-Id: I480b6259f9199b47761dc655a90911eabfe07427
Reviewed-on: https://go-review.googlesource.com/c/go/+/249738
Run-TryBot: Robert Griesemer <a6752097faebf1f02d80107d77a9be009089afe3@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

cloudflare/go,golang/go,nawawi/go,cloudflare/go,cloudflare/go,CAFxX/go,nawawi/go,nawawi/go,CAFxX/go,golang/go,CAFxX/go,CAFxX/go,golang/go,nawawi/go,CAFxX/go,nawawi/go,CAFxX/go,nawawi/go,nawawi/go,nawawi/go,golang/go,cloudflare/go,cloudflare/go,golang/go,cloudflare/go,golang/go,golang/go,cloudflare/go,golang/go,cloudflare/go,CAFxX/go,CAFxX/go