Simplify regex-emacs by assuming Emacs syntax

Simplify regex-emacs by assuming Emacs syntax

* src/regex-emacs.c (reg_syntax_t)
(RE_BACKSLASH_ESCAPE_IN_LISTS, RE_BK_PLUS_QM)
(RE_CHAR_CLASSES, RE_CONTEXT_INDEP_ANCHORS)
(RE_CONTEXT_INDEP_OPS, RE_CONTEXT_INVALID_OPS)
(RE_DOT_NEWLINE, RE_DOT_NOT_NULL, RE_HAT_LISTS_NOT_NEWLINE)
(RE_INTERVALS, RE_LIMITED_OPS, RE_NEWLINE_ALT)
(RE_NO_BK_BRACES, RE_NO_BK_PARENS, RE_NO_BK_REFS)
(RE_NO_BK_VBAR, RE_NO_EMPTY_RANGES)
(RE_UNMATCHED_RIGHT_PAREN_ORD, RE_NO_POSIX_BACKTRACKING)
(RE_NO_GNU_OPS, RE_FRUGAL, RE_SHY_GROUPS)
(RE_NO_NEWLINE_ANCHOR, RE_SYNTAX_EMACS, RE_TRANSLATE_P):
Remove.  All uses removed and resulting code simplified.
(TRANSLATE): Treat nil as an absent translation table, not zero.
All uses changed.