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