Revert "Allow overriding std.Io at a namespace level."
This reverts commit e314dadb015a913a2cdc12298986e9181305d8db.
This idea requires more consideration before committing to it.
At the very least let's not regress autodocs.
Closes #31230
27eec9bd62Andrew Kelley committed on 2/16/2026, 4:26:12 AMparent1838134