cmd/api: omit vendored dependencies when run inside the 'std' module

[cherrymui]

What version of Go are you using (go version)?

tip (b459bc8)

Does this issue reproduce with the latest release?

No.

What did you do?

Currently, at tip (b459bc8), running all.bash, at the end it prints 2000+ lines of new APIs of vendored golang.org/x packages. This is very verbose. And they are not even part of the standard library API, which I thought the API check is for. Could we not emit those? Thanks.

[bcmills]

This is probably somehow related to my changes to the all package pattern. I'll take a look.

[bcmills]

Bisected to CL 251159.

[gopherbot]

Change https://golang.org/cl/254738 mentions this issue: cmd/api: omit outside dependencies when listing the packages in "std"

[cherrymui]

Thanks @bcmills