Revert "Add check to ensure error code explanations are not removed anymore even if not emitted"

This reverts commit 13bdc5c.

Author: pietroalbini

src/ci/docker/host-x86_64/mingw-check/Dockerfile

@@ -28,7 +28,6 @@ COPY scripts/sccache.sh /scripts/
 RUN sh /scripts/sccache.sh
 
 COPY host-x86_64/mingw-check/validate-toolstate.sh /scripts/
-COPY host-x86_64/mingw-check/validate-error-codes.sh /scripts/
 
 ENV RUN_CHECK_WITH_PARALLEL_QUERIES 1
 ENV SCRIPT python3 ../x.py --stage 2 test src/tools/expand-yaml-anchors && \
@@ -38,7 +37,6 @@ ENV SCRIPT python3 ../x.py --stage 2 test src/tools/expand-yaml-anchors && \
            python3 ../x.py test --stage 2 src/tools/tidy && \
            python3 ../x.py doc --stage 0 library/test && \
            /scripts/validate-toolstate.sh && \
-           /scripts/validate-error-codes.sh && \
            # Runs checks to ensure that there are no ES5 issues in our JS code.
            es-check es5 ../src/librustdoc/html/static/js/*.js && \
            eslint ../src/librustdoc/html/static/js/*.js

src/ci/docker/host-x86_64/mingw-check/validate-error-codes.sh

@@ -219,10 +219,6 @@ else
   command="/checkout/src/ci/run.sh"
 fi
 
-# Get some needed information for $BASE_COMMIT
-git fetch "https://github.com/$GITHUB_REPOSITORY" "$GITHUB_BASE_REF"
-BASE_COMMIT="$(git merge-base FETCH_HEAD HEAD)"
-
 docker \
   run \
   --workdir /checkout/obj \
@@ -241,7 +237,6 @@ docker \
   --env TOOLSTATE_PUBLISH \
   --env RUST_CI_OVERRIDE_RELEASE_CHANNEL \
   --env CI_JOB_NAME="${CI_JOB_NAME-$IMAGE}" \
-  --env BASE_COMMIT="$BASE_COMMIT" \
   --init \
   --rm \
   rust-ci \