docs: better pull request template (#3726)

Fixing <br/> showing up in our pull requests since they're basically supposed to be plaintext.

Risk Level: n/a
Testing: n/a
Docs Changes: yep
Release Notes: n/a

Signed-off-by: Alyssa Wilk <alyssar@chromium.org>

PULL_REQUEST_TEMPLATE.md

@@ -1,10 +1,10 @@
 For an explanation of how to fill out the fields, please see the relevant section 
 in PULL_REQUESTS.md
 
-*Description*:<br />
-*Risk Level*:<br />
-*Testing*:<br />
-*Docs Changes*:<br />
-*Release Notes*:<br />
-[Optional Fixes #Issue]<br />
-[Optional *Deprecated*:]<br />
+*Description*:
+*Risk Level*:
+*Testing*:
+*Docs Changes*:
+*Release Notes*:
+[Optional Fixes #Issue]
+[Optional *Deprecated*:]