Revert "This commit adds nsh_consolechild(). I noticed that there are several...

Revert "This commit adds nsh_consolechild().  I noticed that there are several examples that call nsh_consolemain.c to create to create a new NSH session.  That will not always work because nsh_consolemain() performs the one-time initialization needed by the NSH library:  Mounting, reading, and running the start-up script, configuring USB tracing.  Some of those actions will cause failures if attempted twice."

This reverts commit 4d364d83.