I haven't fully confirmed this is sufficient to avoid rebuilds, but I
did confirm for a few packages the version no longer appears in that
package's derivation (which should be sufficient).
We were already setting `commit` to `p.pin` unconditionally, so the
requirement is not new. Add an assert because this can be triggered from
a user packages.el.
Drop url overrides no longer needed because Doom now points at
emacsmirror.
The URL overrides weren't breaking things, because emacsmirror mirrors
these repositories unmodified (the commit Doom pins is present in both).
Exposes what I think is a pre-existing problem with too many directories
getting added to load-path, because we now install a directory
containing a file named "default" that was previously omitted.
trivialBuild results in files installed directly into site-lisp/,
without package metadata. This breaks ELPA packages whose dependencies
we've replaced: package.el refuses to activate the ELPA package because
as far as it knows its dependency is not installed.
melpaBuild seems the easiest way of generating an activatable package
that works with packages we leave untouched.
