Don't repeat title in body of GitHub PR

[steveluscher]

Given a commit of this form:

TITLE

Summary: SUMMARY

Test Plan: TEST_PLAN

Observed behavior

sl pr submit creates a PR with the title TITLE but also repeats that title in the PR description.

Expected behavior

sl pr submit should omit the title from the PR description.

Example PR.

[vegerot]

I actually like this behavior 🤷‍♂️

[vegerot]

On second thought, this feature will be helpful for projects with a required PR Template. I cannot simply use the .github/PULL_REQUEST_TEMPLATE.md because it copies the commit title to the top of the PR description