remove `inTestMode` declaration

Change-Id: I7fa08195db75120df4377c7529d52ba47ff3dcbb
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/331090
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Phil Quitslund <pquitslund@google.com>
Reviewed-by: Samuel Rawlins <srawlins@google.com>
diff --git a/pkg/linter/tool/rule.dart b/pkg/linter/tool/rule.dart
index 44f56ae..875c5c6 100644
--- a/pkg/linter/tool/rule.dart
+++ b/pkg/linter/tool/rule.dart
@@ -270,7 +270,7 @@
 
   sb.write('''
 
-void registerLintRules({bool inTestMode = false}) {
+void registerLintRules() {
   Analyzer.facade.cacheLinterVersion();
   Analyzer.facade
 ''');