ci: re-enable sccache default features

At some point turning off most features used to make things work in our
environments, but looking at things today, I think it basically makes
it do nothing useful any more.

Turning things off just made the image build a hair faster and the
image a hair lighter.

So let's just turn it back on

assets/ci/emit-builder-dockerfile.py

@@ -36,7 +36,7 @@ commands = [
     "/tmp/get-deps.sh",
     "PREFIX=/opt/kumomta /tmp/build-rocksdb.sh",
     f"curl -LsSf {NEXTEST} | tar zxf - -C /usr/local/bin",
-    "cargo install --locked sccache --no-default-features",
+    "cargo install --locked sccache",
     "cargo install --locked xcp",
 ]