gh-84910: Change 'IDLE Help' to 'IDLE Doc' (GH-95873)

'IDLE Help' was a plain text file.  It was superceded years ago
by a copy of the much more complete html doc.  .
(cherry picked from commit 05a0f37029f8ef917ed7ddbf7871856fc73aaca1)

Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>