In #1061 we changed the default command to retry with a simpler find
command with fewer arguments if the first find command failed. This was
to support stripped-down verions of find that do not support -fstype
argument.

However, this caused an unwanted side-effect of yielding duplicate
entries when the first command failed after producing some lines.

We revert the change in this commit, so the default command will not
work with find without -fstype support. But we now print better error
message in that case so that the user can set up a working
$FZF_DEFAULT_COMMAND.

Close #1120 #1167