Bug 4269: ignore-must-revalidate broken

Bug 4269: ignore-must-revalidate broken

ignore-must-revalidate appears to prevent revalidation by disabling
storage of objects with must-revalidate/proxy-revalidate header.

However it was also preventing revalidation of objects cached due to
ignore-private, or the presence of no-cache, s-maxage, and use of auth
credentials.

Remove the violation option entirely.

Also cleanup the documentation of ignore-auth which was removed earlier.