Terraform was redundantly handling `//dir` notation which should be
handled by go-getter. Rather than allowing go-getter to unpack a subdir
as expected, the subdir was stripped off and accessed through the module
configuration.
This scheme will no longer works now that go-getter supports `*`
subdirectories
(e.g. `//*` would be analogous to `tar --strip-components=1`).
Even though this allows Terraform to use go-getter's native unpacking,
detection is still done separately because Detect requires a `pwd` which
is dependent on the configuration directory and not known to the
global FolderStorage.
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