* contrib library unused import removal
* remove a few unused imports.
* another round of unused import removal
* another round of unused import deletion.
* another round of unused import deletion.
The prelude interfaces that have default definitions for all of
their fields are declared total so that users are forced to think
about meeting the minimal requirements for an implementation to be
valid.
This is partly to tidy things up, but also a good test for 'import as'.
Requires some internal changes since there are parts of reflection,
unelaboration and a compiler hack that rely on where things are in the
Prelude.
