Retract #14985, #14899, and #14990, following the principles

Retract #14985, #14899, and #14990, following the principles
"Do no harm." and "If it ain't broke, don't fix it."

Firstly, the #14985 broke badly on UTF-EBCDIC, #14990 fixed
some, but still broken, and I do not have the extra brain
cells for the EBCDIC backport.  Secondly, the old version
worked both in EBCDIC and non-.  Thirdly, the old version
may be more amenable for the behaviour suggsted by Anton
Tagunov regarding the encoding pragma.

p4raw-id: //depot/perl@15084