ext4: remove EXT4_GET_BLOCKS_KEEP_SIZE flag

The eofblocks code was removed in the 5.7 release by "ext4: remove
EOFBLOCKS_FL and associated code" (4337ecd1).  The ext4_map_blocks()
flag used to trigger it can now be removed as well.

Signed-off-by: Eric Whitney <enwlinux@gmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20200415203140.30349-2-enwlinux@gmail.com


Signed-off-by: Theodore Ts'o <tytso@mit.edu>