Improve usage text of get (#3792)

lib/src/command/get.dart

diff --git a/lib/src/command/get.dart b/lib/src/command/get.dart
index 0fc1b6e..bdcc387 100644
--- a/lib/src/command/get.dart
+++ b/lib/src/command/get.dart
@@ -18,6 +18,8 @@
   String get docUrl => 'https://dart.dev/tools/pub/cmd/pub-get';
   @override
   bool get isOffline => argResults['offline'];
+  @override
+  String get argumentsDescription => '';
 
   GetCommand() {
     argParser.addFlag(

test/testdata/goldens/help_test/pub get --help.txt

diff --git a/test/testdata/goldens/help_test/pub get --help.txt b/test/testdata/goldens/help_test/pub get --help.txt
index afd27d5..f2ee2fb 100644
--- a/test/testdata/goldens/help_test/pub get --help.txt
+++ b/test/testdata/goldens/help_test/pub get --help.txt
@@ -4,7 +4,7 @@
 $ pub get --help
 Get the current package's dependencies.
 
-Usage: pub get <subcommand> [arguments...]
+Usage: pub get
 -h, --help                Print this usage information.
     --[no-]offline        Use cached packages instead of accessing the network.
 -n, --dry-run             Report what dependencies would change but don't change any.