ld: remove stray debug fprintf

In this commit:

  commit ace667e5
  Date:   Mon Jul 18 21:00:00 2016 +0100

      ld: Restore file offset after a plugin fails to claim a file

I inadvertently left in a stray fprintf call.  Removed in this commit.

ld/ChangeLog:

	* testplugin.c (record_read_length): Remove debug fprintf.