[cfe] Remove unnecessary_null_comparison code

The frontend is now run with sound null safety so these are no longer needed.

TEST=existing

Change-Id: I6c1776845854695ff34e310a3bb5bc9d86715f06
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/307901
Reviewed-by: Jens Johansen <jensj@google.com>
Reviewed-by: Srujan Gaddam <srujzs@google.com>
Reviewed-by: Alexander Markov <alexmarkov@google.com>
Commit-Queue: Johnni Winther <johnniwinther@google.com>

pkg/testing/lib/src/error_handling.dart

@@ -20,10 +20,7 @@ Future<T?> withErrorHandling<T>(Future<T> Function() f,
   } catch (e, trace) {
     exitCode = 1;
     stderr.writeln(e);
-    // ignore: unnecessary_null_comparison
-    if (trace != null) {
-      stderr.writeln(trace);
-    }
+    stderr.writeln(trace);
     logger?.noticeFrameworkCatchError(e, trace);
     return null;
   } finally {

pkg/testing/lib/src/log.dart

@@ -198,10 +198,7 @@ class StdoutLogger implements Logger {
   @override
   void logUncaughtError(error, StackTrace stackTrace) {
     logMessage(error);
-    // ignore: unnecessary_null_comparison
-    if (stackTrace != null) {
-      logMessage(stackTrace);
-    }
+    logMessage(stackTrace);
   }
 
   @override