'text-quoting-style' now affects only ` and '

'text-quoting-style' now affects only ` and '

Change 'text-quoting-style' so that it no longer affects
formatting of curved quotes in format arguments to functions like
'message'.  In particular, when this variable's value is 'grave',
all quotes in formats are output as-is.
* doc/lispref/help.texi (Keys in Documentation):
* doc/lispref/strings.texi (Formatting Strings):
* doc/lispref/tips.texi (Documentation Tips):
* etc/NEWS:
* src/doc.c (syms_of_doc): Document this.
* lisp/help-fns.el (describe-function-1):
* src/doc.c (text_quoting_style, Fsubstitute_command_keys)
(syms_of_doc):
* src/editfns.c (styled_format): Omit now-unnecessary code.
* src/lisp.h (LEAVE_QUOTING_STYLE): Remove.