Remove explicit dependency on amqplib

amqp (or amqplib) is only accessed via kombu, and kombu
already specifies the right dependency (either amqp if new
enough or amqplib for old versions of kombu).

Change-Id: I4efa419db1befdfcbe639a8557e21eb97ca3a26e
Merge "Remove explicit dependency on amqplib"