gnu: sbcl-stumpwm: Drop ECL lisp support and rename to 'stumpwm'.

gnu: sbcl-stumpwm: Drop ECL lisp support and rename to 'stumpwm'.

StumpWM version 1.0.0 was the last version to support lisps other than SBCL.
This patch renames the current version of Stumpwm to simply 'stumpwm' instead
of 'sbcl-stumpwm' since it's redundant, and removes the unmaintained
'ecl-stumpwm' package.

* gnu/packages/lisp.scm (sbcl-stumpwm): Deprecate in favor of 'stumpwm'.
[name]: Rename to 'stumpwm'.
[arguments]: Set '#:asd-system-name' to 'stumpwm'.
[properties]: Replace ecl-variant with cl-source-variant.
(ecl-stumpwm): Remove variable.
(cl-stumpwm): Replace 'sbcl-stumpwm' with 'stumpwm' and adapt.
(sbcl-stumpwm+slynk): Deprecate in favor of 'stumpwm+slynk'.
[name]: Rename to 'stumpwm-with-slynk'.
[inherit, inputs, arguments]: Replace 'sbcl-stumpwm' with 'stumpwm'.

Signed-off-by: Oleg Pykhalov <go.wigust@gmail.com>