Remove --crate-type=metadata from beta

[nrc]

Leaves most of the implementation, just ignores the argument itself.

r? @alexcrichton

[rust-highfive]

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[nrc]

cc #38666

[alexcrichton]

@nrc oh one thing I just thought of was also #![crate_type = "metadata"], do we need to update something somewhere to also not accept that? Or is that handled here as well?

[nrc]

@alexcrichton That is handled here too.

[alexcrichton]

Ok!