ed: clean some redundant code

[mknos]

• In edMove(), special code isn't needed for $count of one because the .. operator can handle 1..1
• edPrint() already relies on this because it loops with "$adrs[0] .. $adrs[1]", where both can be equal
• Tested with command "1m20" to move the 1st line in buffer ($end is inferred from $start)
• Remove chmod() comment in edWrite(); OpenBSD version does not perform chmod() and that is a better reference
• Standards document mentions nothing about changing file modes/permissions[1]
• In edHelp() the saved error will be printed each time the "H" command enables the help flag; avoid extra return statement

1. https://pubs.opengroup.org/onlinepubs/9699919799/utilities/ed.html

[briandfoy]

changes: clean up some internals