build: remove qt libjpeg check from bitcoin_qt.m4

Summary:
Was last used in 2013.

Backport of core PR16441.

Depends on D5638.

Test Plan: Run the Gitian builds.

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D5639