gnu: emacs-ess: Update to 18.10.2-0.24da603.

* gnu/packages/statistics.scm (emacs-ess): Update to 18.10.2-0.24da603.
[version]: Use version-revision-commit for version numbering.
[source]: Fix snippet for removing julia-mode.  Remove snippet to modify
roxy-preview-Rd-test.  Add snippet to modify r-help-mode test.  Add
snippet to fix install target to install files to correct directories.
Correct Makefile so that ess-autoloads.el is not built twice.
[arguments]: Add flag to specify INFODIR.  Remove patch modifying SHELL.
[license]: License is now GPLv3+.

Signed-off-by: Nicolas Goaziou <mail@nicolasgoaziou.fr>