Remove arc_mail_parse()

This has no tests or internal usage, is not directly useful for
integrating ARC, and at best implements an outdated version of this
parsing.

CHANGELOG.md

@@ -34,6 +34,9 @@ All notable changes to this project will be documented in this file.
 - milter - An `ar-test` program for seeing how `Authentication-Results`
   headers are parsed is built without making you jump through weird hoops.
 
+### Removed
+- libopenarc - `arc_mail_parse()`
+
 ### Fixed
 - libopenarc - Seals on failed chains only cover the latest ARC header set,
   as required by [RFC 8617 section 5.1.2](https://datatracker.ietf.org/doc/html/rfc8617#section-5.1.2).

Makefile.am

@@ -34,8 +34,6 @@ libopenarc_libopenarc_la_SOURCES = \
 	libopenarc/arc-internal.h \
 	libopenarc/arc-keys.c \
 	libopenarc/arc-keys.h \
-	libopenarc/arc-mailparse.c \
-	libopenarc/arc-mailparse.h \
 	libopenarc/arc-tables.c \
 	libopenarc/arc-tables.h \
 	libopenarc/arc-types.h \