Remove last two references to Cirrus CI. (#161530)

Towards https://github.com/flutter/flutter/issues/161387.

dev/devicelab/lib/framework/running_processes.dart

@@ -145,11 +145,6 @@ Future<Set<RunningProcessInfo>> posixRunningProcesses(
   String? processName,
   ProcessManager processManager,
 ) async {
-  // Cirrus is missing this in Linux for some reason.
-  if (!processManager.canRun('ps')) {
-    print('Cannot list processes on this system: "ps" not available.');
-    return <RunningProcessInfo>{};
-  }
   final ProcessResult result = await processManager.run(<String>[
     'ps',
     '-eo',

engine/src/flutter/testing/benchmark/bin/parse_and_send.dart

@@ -15,8 +15,6 @@ Future<ProcessResult> runGit(List<String> args, {String? processWorkingDir}) asy
 
 Future<List<String>> getGitLog() async {
   final String gitRoot = p.absolute('../..');
-  // Somehow gitDir.currentBranch() doesn't work in Cirrus with "fatal: 'HEAD' -
-  // not a valid ref". Therefore, we use "git log" to get the revision manually.
   final ProcessResult logResult = await runGit(<String>[
     'log',
     '--pretty=format:%H %ct',