(byte-compile-version-cond): Remove macro.

(byte-compile-version-cond): Remove macro.
(byte-compile-compatibility): Remove option.
(byte-compile-close-variables, byte-compile-fix-header)
(byte-compile-insert-header, byte-compile-output-docform)
(byte-compile-file-form-defmumble, byte-compile-byte-code-maker)
(byte-compile-lambda, byte-compile-form, byte-defop-compiler19)
(byte-compile-list, byte-compile-concat, byte-compile-function-form)
(byte-compile-insert, byte-compile-defun):
Remove support for byte-compile-compatibility and Emacs 18.  (Bug#4571)