bump libevent to 2.1.11 in depends
Summary:
this doesn't need patches on Android anymore like 2.1.8 did.
Backport of core PR17008.
Test Plan: Run the Gitian builds.
Reviewers: #bitcoin_abc, deadalnix
Reviewed By: #bitcoin_abc, deadalnix
Differential Revision: https://reviews.bitcoinabc.org/D5671