Do not allow: dart pub token remove --no-all (#3116)

diff --git a/lib/src/command/token_remove.dart b/lib/src/command/token_remove.dart
index 5db8d51..7c49a0d 100644
--- a/lib/src/command/token_remove.dart
+++ b/lib/src/command/token_remove.dart
@@ -23,7 +23,11 @@
   bool get isAll => argResults['all'];
 
   TokenRemoveCommand() {
-    argParser.addFlag('all', help: 'Remove all secret tokens.');
+    argParser.addFlag(
+      'all',
+      negatable: false,
+      help: 'Remove all secret tokens.',
+    );
   }
 
   @override