Delete rabbit_uri

[ansd]

Since #13242 updated Cowlib to v2.14.0, this commit deletes rabbit_uri as written in the comments of rabbit_uri.erl:

This file is a partial copy of
https://github.com/ninenines/cowlib/blob/optimise-urldecode/src/cow_uri.erl
We use this copy because:
1. uri_string:unquote/1 is lax: It doesn't validate that characters that are
   required to be percent encoded are indeed percent encoded. In RabbitMQ,
   we want to enforce that proper percent encoding is done by AMQP clients.
2. uri_string:unquote/1 and cow_uri:urldecode/1 in cowlib v2.13.0 are both
   slow because they allocate a new binary for the common case where no
   character was percent encoded.
When a new cowlib version is released, we should make app rabbit depend on
app cowlib calling cow_uri:urldecode/1 and delete this file (rabbit_uri.erl).