* guix-kernel/environ.scm: Rename to...
* guix/jupyter/environ.scm: ... this.
* guix-kernel/magic.scm: Rename to...
* guix/jupyter/magic.scm: ... this
* guix-jupyter-container.scm, guix-jupyter-kernel.scm,
tests/environ.scm, tests/magic.scm: Adjust accordingly.
* Makefile.am (SOURCES): Adjust accordingly.