fix(guix): restore MPL-2.0 -- the squisher clobber downgraded it to PMPL

guix.scm declared (license ... "PMPL-1.0-or-later") while its OWN SPDX header
on line 1 said MPL-2.0, and the repo's root LICENSE is the Mozilla Public
License. The file contradicted itself: the signature of the squisher-corpus
clobber, which wrote one package definition across the estate carrying another
project's identity and licence.

Measured across all 418 estate repos: 64 guix.scm files asserted PMPL. Exactly
2 were self-consistent (SPDX header ALSO PMPL) and are untouched --
palimpsest-license and polystack. The other 62, including this one, were
contradictory.

Now uses Guix's built-in `mpl2.0` rather than the hand-rolled licence record,
which also removes the palimpsest-license URL that had no business on an
MPL-2.0 package.

Verified: no PMPL remains, and the file still parses as Scheme.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: hyperpolymath

guix.scm

@@ -14,5 +14,4 @@
   (synopsis "nextgen-typing")
   (description "nextgen-typing — part of the hyperpolymath ecosystem.")
   (home-page "https://github.com/hyperpolymath/nextgen-typing")
-  (license ((@@ (guix licenses) license) "PMPL-1.0-or-later"
-             "https://github.com/hyperpolymath/palimpsest-license")))
+  (license mpl2.0))