gfs2_tool: Fix build warnings in misc.c bz 441636
    
    gfs2_tool used to include both linux/fs.h and sys/mount.h that caused some symbols to be defined twice and hence caused some build warnings. This patch uses linux/ext3_fs.h instead of /linux/fs.h and uses EXT3_XXX_FL inode flags instead of the respective FS_XXX_FL flags.
    This patch also removes the SYSTEM and DIRECTIO flags as they are not used anymore.