Remove puts_debug

Remove puts_debug

I noticed that puts_debug isn't used in the tree.  git log tells me
that the last use was removed in 2015:

    commit 40e0b27177e747600d3ec186458fe0e482a1cf77
    Author: Pedro Alves <palves@redhat.com>
    Date:   Mon Aug 24 15:40:26 2015 +0100

	Delete the remaining ROM monitor targets

... and this commit mentions that the code being removed here probably
hadn't worked for 6 years prior to that.

Based on this, I'm removing puts_debug.  I don't think it's useful.
Tested by rebuilding.