Add function to delete pending reviews on a pull request (#1897)

Add a delete method to PullRequestReview to allow dismissing them.

Fixes #1856 

Co-authored-by: bagashvilit <bagashvilit@allegheny.edu>
Co-authored-by: WonjoonC <chos@allegheny.edu>

github/PullRequestReview.py

@@ -105,6 +105,15 @@ class PullRequestReview(github.GithubObject.NonCompletableGithubObject):
             input=post_parameters,
         )
 
+    def delete(self):
+        """
+        :calls: `DELETE /repos/:owner/:repo/pulls/:number/reviews/:review_id <https://developer.github.com/v3/pulls/reviews/>`_
+        :rtype: None
+        """
+        headers, data = self._requester.requestJsonAndCheck(
+            "DELETE", f"{self.pull_request_url}/reviews/{self.id}"
+        )
+
     def _initAttributes(self):
         self._id = github.GithubObject.NotSet
         self._user = github.GithubObject.NotSet

github/PullRequestReview.pyi

@@ -13,6 +13,7 @@ class PullRequestReview(CompletableGithubObject):
     @property
     def commit_id(self) -> str: ...
     def dismiss(self, message: str) -> None: ...
+    def delete(self) -> None: ...
     @property
     def html_url(self) -> str: ...
     @property