Delete the Janet host — Chez is the sole substrate

Remove the Janet seed (src/jolt/*.janet: reader, value layer, vars/ns, the
tree-walking interpreter, the Janet backend, the optimizing compiler), the
Janet->Scheme cross-compiler (host/chez/{driver,emit,jolt-chez}.janet),
bin/jolt-chez, the jpm build (project.janet) and the Janet test runner
(run-tests.janet), plus the entire Janet test suite. jolt now builds and runs
on Chez alone: bin/joltc off the checked-in seed, bootstrap.ss to rebuild it.

The portable Clojure stays: jolt-core/**, host/chez/**.ss, and the stdlib +
tooling under src/jolt/clojure + src/jolt/jolt (read by the seed build, no
Janet). The gate is 'make test' (self-host, corpus, unit, cli smoke, certify).
Drop the sci and clojure-test-suite submodules (used only by deleted Janet
integration tests); irregex stays.

Filesystem corpus/unit cases that probed project.janet now probe README.md.

jolt-cf1q.6

.gitmodules

@@ -1,9 +1,3 @@
-[submodule "vendor/sci"]
-	path = vendor/sci
-	url = https://github.com/borkdude/sci.git
-[submodule "vendor/clojure-test-suite"]
-	path = vendor/clojure-test-suite
-	url = https://github.com/jank-lang/clojure-test-suite.git
 [submodule "vendor/irregex"]
 	path = vendor/irregex
 	url = https://github.com/ashinn/irregex.git