runtime/cgo: do not change directory during runtime/cgo init

[bcmills]

In CL 8784, runtime/cgo on ios was given special-case code to change the current working directory to the app root.

That high-level behavior seems awfully presumptuous and out-of-place in a low-level package like runtime/cgo, and it causes runtime/cgo to depend on the CoreFoundation framework on ios when it does not need that framework on other darwin platforms.

If the init_working_dir behavior belongs in the standard library at all, arguably an init function in the os package would be much more appropriate than an ad-hoc side effect in runtime/cgo.

(attn @golang/ios; CC @golang/runtime)

[bcmills]

Concretely, this special case complicates things like misc/cgo/testcarchive, which then needs its own special-case code to deal with the inappropriate dependency.

Moreover, it causes a Go library linked into a larger ios program to change the current working directory, which is not at all an appropriate library behavior!

[gopherbot]

Change https://go.dev/cl/463752 mentions this issue: cmd/dist,internal/platform: reenable the c-archive build mode on ios