gnu: racket: Update to 8.8.
* gnu/packages/patches/racket-backport-8.7-pkg-strip.patch: Remove file.
* gnu/local.mk (dist_patch_DATA): Delete it.
* gnu/packages/racket.scm (%racket-origin)[patches]: Likewise.
(%racket-version): Update to 8.8.
(%zuo-version): Update to 1.6.
(racket)[inputs]<algol60, cext-lib, deinprogramm, draw, drracket>
<expeditor, gui, htdp, math, pict, r5rs, redex, sasl, scribble>
<typed-racket, string-constants, syntax-color>: Update checksums.
* gnu/packages/chez.scm (chez-scheme-for-racket): Update to
9.9.9-pre-release.14.
Signed-off-by: Liliana Marie Prikler <liliana.prikler@gmail.com>