gnu: Rename "guile-next" to "guile".

gnu: Rename "guile-next" to "guile".

* gnu/packages/guile.scm (guile-next): Rename to...
(guile-2.2): ... this.  Update users.
[name]: Change to "guile".
[synopsis]: Remove.
[properties]: Remove 'upstream-name', 'ftp-server', and
'ftp-directory'.
* gnu/packages/bioinformatics.scm (rcas-web): Update accordingly.
* gnu/packages/tls.scm (gnutls/guile-2.2): Likewise.
* tests/guix-build.sh: Use 'guile@2.2' instead of 'guile-next'.
* doc/guix.texi (Package Transformation Options): Update examples that
referred to "guile-next".