ibuf_read_merge_pages(): Disable some code that was added in MDEV-20394
in order to avoid a server hang if the change buffer is corrupted,
presumably due to the race condition in recovery that was later fixed in
MDEV-24449. The code will still be available in debug builds when
the command line option --debug=d,ibuf_merge_corruption is specified.

Due to MDEV-19514, the impact of this code is much worse starting
with the 10.5 series. In older versions, the code was only enabled
during a shutdown with innodb_fast_shutdown=0, but in 10.5 it was
active during the normal operation of the server.