change platform from per-distro subdirectories to release folder, wit…

…h platform in filename

tools/release_engineering/dev/push_release

@@ -98,10 +98,8 @@ if [[ "${push_apt}" -ne 0 ]]; then
     mkdir -p "${platform}"
     pushd "${platform}"
 
-    filename="drake-dev_${source_version}-1_amd64.deb"
-
     curl --fail --location --remote-name \
-      "https://drake-packages.csail.mit.edu/drake/release/${platform}/${filename}"
+      "https://drake-packages.csail.mit.edu/drake/release/drake-dev_${source_version}-1_amd64-${platform}.deb"
 
     # Add the Debian package to the aptly database.
     aptly repo add "drake-${platform}" "${filename}"

tools/release_engineering/dev/push_release.py

@@ -354,9 +354,8 @@ def _push_deb(state: _State):
     Downloads .deb artifacts and push them to S3.
     """
     for deb in state.find_artifacts(_Manifest.RE_DEB):
-        dest_name = f'drake-dev_{deb.version}_{deb.arch}.{deb.ext}'
-        dest_path = f'drake/release/{deb.platform}/{dest_name}'
-        state.push_artifact(deb, _AWS_BUCKET, dest_path)
+        dest_name = f'drake/release/drake-dev_{deb.version}_{deb.arch}-{deb.platform}.{deb.ext}'
+        state.push_artifact(deb, _AWS_BUCKET, dest_name)
 
 
 def _push_docker(state: _State):