It is no longer necessary to produce `.swiftinterface` files the support older
compilers that lack support for the NoncopyableGenerics feature. Cleaning this
up makes the stdlib `.swiftinterface` far more readable.
If the extension adds conformance to an invertible protocol, it's
confusing for people to also infer conditional requirements on the
generic parameters for those invertible protocols. This came up in the
review of SE-427.
These tests were not updated in the transition to
`REQUIRES: noncopyable_generics` and thus running them with a
correctly-built stdlib that has the Copyable requirements.
A swiftmodule can only be correctly ingested by a compiler
that has a matching state of using or not-using
NoncopyableGenerics.
The reason for this is fundamental: the absence of a Copyable
conformance in the swiftmodule indicates that a type is
noncopyable. Thus, if a compiler with NoncopyableGenerics
reads a swiftmodule that was not compiled with that feature,
it will think every type in that module is noncopyable.
Similarly, if a compiler with NoncopyableGenerics produces a
swiftmodule, there will be Copyable requirements on each
generic parameter that the compiler without the feature will
become confused about.
The solution here is to trigger a module mismatch, so that
the compiler re-generates the swiftmodule file using the
swiftinterface, which has been kept compatible with the compiler
regardless of whether the feature is enabled.
