Don't set SOURCE_DATE_EPOCH at all

It isn't helping make anything more reproducible, setting it so late.
We'll file a bug about `.pyc` reproducibility, later.

Author: stefanor

.github/workflows/reusable-ubuntu.yml

@@ -131,10 +131,6 @@ jobs:
       run: xvfb-run make ci EXTRATESTOPTS="${TEST_OPTS}"
       env:
         TEST_OPTS: ${{ inputs.test-opts }}
-    - name: Use the commit timestamp for timestamps the install
-      # we do this after test execution, as some tests are broken by it. GH-154948
-      if: inputs.upload-install-hashes
-      run: echo "SOURCE_DATE_EPOCH=$(git log -1 --format=%ct)" >> $GITHUB_ENV
     - name: Install Python
       if: inputs.upload-install-hashes
       working-directory: ${{ env.CPYTHON_BUILDDIR }}