qt: Get rid of cursor in out-of-focus labels

Summary:
This change is a temporary fix of QTBUG-59514.

This is a backport of core#19210

Test Plan:
ninja all check-all
src/qt/bitcoin-qt
I wasn't able to reproduce the bug, so I just checked that everything
still works as before. I suspect this only affects some versions of Qt.

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D10005