Don't test for escaped delimiters in rainbow-delimiters--face-propertize*.

They're marked by rainbow-delimiters--category-propertize, so the
rainbow-delimiters--for-all-delimiters call in
rainbow-delimiters--face-propertize* will not even see them.
Remove redundant test.

rainbow-delimiters--escaped-char-predicate-emacs-lisp doesn't have
to test for backslash-escaped delimiters, because the syntax table
based test in rainbow-delimiters--char-ineligible-p already catches them.