Revert "Backport: work around GitHub .patch URL issue (dotnet#74452)" (dotnet#76659)

This reverts commit 96a32c6.

Author: akoeplinger

eng/actions/backport/index.js

@@ -67,9 +67,7 @@ async function run() {
     } catch { }
 
     // download and apply patch
-    let patch_url = github.context.payload.issue.pull_request.patch_url;
-    patch_url = patch_url.replace("runtime", "RUNTIME");
-    await exec.exec(`curl -sSL "${patch_url}" --output changes.patch`);
+    await exec.exec(`curl -sSL "${github.context.payload.issue.pull_request.patch_url}" --output changes.patch`);
 
     const git_am_command = "git am --3way --ignore-whitespace --keep-non-patch changes.patch";
     let git_am_output = `$ ${git_am_command}\n\n`;