adb: remove incorrect use of RTTI.

We were dynamic_casting to UsbConnection to check for USB connections,
but the actual type was a BlockingConnectionAdapter wrapping a
UsbConnection, with the result that unplugging an inaccessible (due to
permissions) device on Linux wouldn't make the device go away.

Test: manual
Change-Id: Icb4acea5fd3c3baa9691698686213e122e898e4a
diff --git a/adb/transport.cpp b/adb/transport.cpp
index 8741654..f59a135 100644
--- a/adb/transport.cpp
+++ b/adb/transport.cpp
@@ -1305,11 +1305,7 @@
 void unregister_usb_transport(usb_handle* usb) {
     std::lock_guard<std::recursive_mutex> lock(transport_lock);
     transport_list.remove_if([usb](atransport* t) {
-        auto connection = t->connection();
-        if (auto usb_connection = dynamic_cast<UsbConnection*>(connection.get())) {
-            return usb_connection->handle_ == usb && t->GetConnectionState() == kCsNoPerm;
-        }
-        return false;
+        return t->GetUsbHandle() == usb && t->GetConnectionState() == kCsNoPerm;
     });
 }
 #endif