service: Address lint issues

Specifically,
 C0301: Line too long (83/80) (line-too-long)
 W0612: Unused variable 'branch' (unused-variable)

BUG=none
TEST=./run_tests

Change-Id: I9bd90b67a9f87a0dc156f2ae95733580b2d6e97a
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/6272841
Commit-Queue: Jae Hoon Kim <kimjae@chromium.org>
Tested-by: Jae Hoon Kim <kimjae@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
diff --git a/service/packages.py b/service/packages.py
index 5a19117..0f75e91 100644
--- a/service/packages.py
+++ b/service/packages.py
@@ -1311,9 +1311,9 @@
 
     For instance:
 
-    GS_MIRROR/distfiles/starbase-head-20230101-r00-rc001/starbase-foobar.tar.zst
+    GS_MIRROR/distfiles/starbase-head-20230101-r00-rc001/starbase-foo.tar.zst
     or
-    GS_MIRROR/distfiles/starbase-release-20230101-r00-rc001/starbase-foobar.tar.zst
+    GS_MIRROR/distfiles/starbase-release-20230101-r00-rc001/starbase-foo.tar.zst
 
     Note that each directory can contain multiple tar files.  The "refs"
     parameter is a list with one element for each tar file (or package).  Only
@@ -1341,9 +1341,9 @@
         # We're ignoring the meaning of the `ref` fields and reusing them for
         # our purposes.  See absurdly long comment above.
         tarfile_name, tarfile_hash = ref.path.split("/", 1)
-        branch = ""
         if len(ref.ref.split("/")) == 3:
-            branch, category, package_name = ref.ref.split("/", 2)
+            # First in the split is the "branch".
+            _, category, package_name = ref.ref.split("/", 2)
         else:
             category, package_name = ref.ref.split("/", 1)
         # Helium ARCVM artifacts uprev the ebuild in the Helium overlay.