[skip ci]Remove pull request template (#7777)

Signed-off-by: Xiangyu Wang <xiangyu.wang@zilliz.com>

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,17 +0,0 @@
-Explain the problem that this commit is solving. Focus on why you
-are making this change as opposed to how (the code explains that).
-Are there side effects or other unintuitive consequences of this
-change? Here's the place to explain them.
-
-Further paragraphs come after blank lines.
-
- - Bullet points are okay, too
-
- - Typically a hyphen or asterisk is used for the bullet, preceded
-   by a single space, with blank lines in between, but conventions
-   vary here
-
-Resolves: #<issue_id>, #<issue_id>
-See also: #<related_issue_or_pr_id>
-
-Signed-off-by: <username> <mail>