remove gotypesalias, asynctimerchan GODEBUG flag for 1.27

[griesemer]

I propose that we pre-announce in the Go 1.26 release notes the removal in Go 1.27 of the following GODEBUG flags:

• gotypesalias introduced in Go 1.22
• asynctimerchan introduced in Go 1.23

[gabyhelp]

Related Issues

• proposal: policy for removing GODEBUG flags #76163
• crypto: remove in Go 1.27 GODEBUGs introduced in Go 1.23 and earlier #75316

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[aclements]

This proposal has been added to the active column of the proposals project
and will now be reviewed at the weekly proposal review meetings.
— aclements for the proposal review group

[gopherbot]

Change https://go.dev/cl/726020 mentions this issue: doc: pre-announce removal of gotypesalias and asynctimerchan GODEBUG flags

[aclements]

Based on the discussion above, this proposal seems like a likely accept.
— aclements for the proposal review group

The proposal is given in #76472 (comment)