.github/workflows: Drop sourcegraph LSIF task.

The LSIF uploader has been superseded by the SCIP uploader, and it seems to take
more effort to set up.

GitHub's code search has improved recently and I barely use SourceGraph anymore,
so just drop it. It can be added back if the need arises in future.

.github/workflows/ci.yml

@@ -158,16 +158,3 @@ jobs:
       run: pip3 install beautifulsoup4
     - name: Check relative links
       run: make -C website check-rellinks
-
-  lsif:
-    name: Upload SourceGraph LSIF
-    if: github.repository == 'elves/elvish' && github.event_name == 'push'
-    runs-on: ubuntu-latest
-    container: sourcegraph/lsif-go:latest
-    steps:
-    - name: Checkout code
-      uses: actions/checkout@v4
-    - name: Generate LSIF data
-      run: lsif-go
-    - name: Upload LSIF data
-      run: src lsif upload -github-token=${{ secrets.GITHUB_TOKEN }} -ignore-upload-failure