Delete rtc::PacketTime (was an alias for int64_t)

Followup to https://webrtc-review.googlesource.com/c/91860.

Bug: webrtc:9584
Change-Id: Icadf73d6c275ef32167357fc33b3c08158fa096f
Reviewed-on: https://webrtc-review.googlesource.com/c/114545
Reviewed-by: Steve Anton <steveanton@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26109}

rtc_base/asyncpacketsocket.h

@@ -12,7 +12,6 @@
 #define RTC_BASE_ASYNCPACKETSOCKET_H_
 
 #include "rtc_base/constructormagic.h"
-#include "rtc_base/deprecation.h"
 #include "rtc_base/dscp.h"
 #include "rtc_base/network/sent_packet.h"
 #include "rtc_base/socket.h"
@@ -52,10 +51,6 @@ struct PacketOptions {
   PacketInfo info_signaled_after_sent;
 };
 
-// TODO(bugs.webrtc.org/9584): Compatibility alias, delete as soon as downstream
-// code is updated.
-typedef int64_t PacketTime;
-
 // Provides the ability to receive packets asynchronously. Sends are not
 // buffered since it is acceptable to drop packets under high load.
 class AsyncPacketSocket : public sigslot::has_slots<> {