gnu: racket: Racket inherits racket-minimal, not vice versa.

gnu: racket: Racket inherits racket-minimal, not vice versa.

By design, the `racket` package is equivalent to 'racket-minimal'
plus 'raco pkg install -i main-distribution'.
This switch brings the Guix packages a small step closer to that goal.

* gnu/packages/racket.scm (racket-minimal, racket): Change
'racket-minimal' to be the base package and 'racket' to inherit
from it.  Move 'version', 'patches', 'home-page', 'build-system',
'arguments', and 'license' to 'racket-minimal'.
* gnu/packages/racket.scm (racket)[inputs]: Rather than copy and
pasting, use '(package-inputs racket-minimal)'.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>