Allowing ProxyActivityStarter without result.

This is required in some cases, when we do not want
the Launcher (ProxyActivityStarter) Activity to come
in recents.

Bug: 320664417
Flag: ACONFIG com.android.launcher3.private_space_app_installer_button TEAMFOOD
Test: Manual build and flash.
Change-Id: I94d9dfab19f8a2410fa82adc0c0c22a3ac238a0b