git-commit-proxy-version: Omit SHAs from commit (#3076)

The git-commt-proxy-version script attempted to link to the specifc
SHAs. GitHub doesn't actually render these links, and the information is
redundant since we link the appropriate PR.

bin/git-commit-proxy-version

@@ -35,7 +35,7 @@ echo "proxy: Update proxy to ${new_proxy_revision}" >"$tmp/commit.template"
 echo "" >>"$tmp/commit.template"
 
 git log --pretty=oneline --abbrev-commit --reverse "${old_proxy_version}..${new_proxy_version}" | \
-sed -E -e 's,^,* linkerd/linkerd2-proxy#,' \
+    sed -E -e 's,^[a-f0-9]{7} ,* ,' \
     -e 's, \((#[0-9]+)\), (linkerd/linkerd2-proxy\1),' \
     >>"$tmp/commit.template"