Disable text conversion within read-char-from-minibuffer

Disable text conversion within read-char-from-minibuffer

* lisp/subr.el (read-char-from-minibuffer): Disable text
conversion.  (bug#65370)
(y-or-n-p): Remove redundant binding of
`override-text-conversion-style', given that read-key already
disables text conversion.

* src/textconv.c (Fset_text_conversion_style): Always reset text
conversion for the selected frame in addition to any displaying
current_buffer.