Remove space check from overlayfs test

This check means that drives are remounted with overlayfs more or less
at random, which means that overlayfs_remounter selinux policy will have
to be very permissive to support all possible remounts.

Test: system/core/fs_mgr/tests/adb-remount-test.sh, confirmation from
reporter that this does indeed fix their issue

Bug: 394657884
Change-Id: I2b340f5df1a609ad5b8e2214bbe7afddec23ca31