Remove workaround for MDEV-13941, it served for 5 years,and all affected
pre-release 10.2 installation should have been already fixed in between.
Apparently Innodb is using is_sparse parameter in os_file_set_size()
inconsistently, and it passes is_sparse=false now during first file
extension. With MDEV-13941 workaround in place, it would unsparse
the file, which is makes compression not to work at all anymore.
