Delete leftover mention of AsyncInvoker

Bug: None
Change-Id: I8900873f096225fecfbb2115642fa16178078db6
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/189545
Reviewed-by: Sebastian Jansson <srte@webrtc.org>
Reviewed-by: Sami Kalliomäki <sakal@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#32440}

api/test/DEPS

@@ -11,11 +11,6 @@ specific_include_rules = {
   "fake_constraints\.h": [
     "+rtc_base/string_encode.h",
   ],
-  "loopback_media_transport\.h": [
-    "+rtc_base/async_invoker.h",
-    "+rtc_base/thread.h",
-    "+rtc_base/thread_checker.h",
-  ],
   "neteq_factory_with_codecs\.h": [
     "+system_wrappers/include/clock.h",
   ],