emacs-jabber.rcp: avoid shell-interpolation in :build commands

Fixes these warnings during emacs-jabber installation:

```
Warning (emacs): Build command "autoreconf -i" in package "emacs-jabber" will be shell-interpolated. To bypass shell interpolation, the recipe for "emacs-jabber" should specify build commands as lists of strings instead.
Warning (emacs): Build command "mv jabber.info emacs-jabber.info" in package "emacs-jabber" will be shell-interpolated. To bypass shell interpolation, the recipe for "emacs-jabber" should specify build commands as lists of strings instead.

```