remove archived error-chain crate from integration tests

Can't run `cargo test --all` for `error-chain` anymore. The tests don't
compile because of `#[deny(invalid_doc_attributes)]`. Here's  the error
message:

```
error: this attribute can only be applied at the crate level
   --> tests/tests.rs:508:7
    |
508 | #[doc(test)]
    |       ^^^^
    |
    = note: read <https://doc.rust-lang.org/nightly/rustdoc/the-doc-attribute.html#at-the-crate-level> for more information
    = note: `#[deny(invalid_doc_attributes)]` on by default
help: to apply to the crate, use an inner attribute
    |
508 | #![doc(test)]
    |  +
```

.github/workflows/integration.yml

@@ -19,7 +19,6 @@ jobs:
       matrix:
         integration: [
           bitflags,
-          error-chain,
           log,
           mdbook,
           packed_simd,

ci/integration.sh

@@ -104,7 +104,7 @@ case ${INTEGRATION} in
         check_fmt_with_all_tests
         cd -
         ;;
-    error-chain | tempdir)
+    tempdir)
         git clone --depth=1 https://github.com/rust-lang-deprecated/${INTEGRATION}.git
         cd ${INTEGRATION}
         show_head