Remove Batcache references in messaging

[rebeccahum]

VIP Go does not utilize Batcache and we overwrite the messaging in the ruleset anyways, so I think we can clean it up a bit and remove the Batcache references.

#613 is related as well.

[GaryJones]

LGTM.

To summarise the changes here, as I see it:

• Original sniffs were written for WPCOM, and so mentioned Batcache.
• The error messages were overridden in WordPress-VIP-Go ruleset to make them more generic (since Batcache isn't used there).
• Since we no longer have any WPCOM, then the original sniff messages can be updated to be more generalised, and the ruleset overrides can be removed.

[jrfnl]

Reviewed after the fact.

Notes:

• The change to the WordPressVIPMinimum.Functions.RestrictedFunctions cookies group is good, though there are some comments in the ruleset test case files which will still need to be updated.
  Note: this change will need a changelog entry as a warning has changed to error for the WordPressVIPMinimum standard.
• While not used in the VIP-Go standard, the message text for the WordPressVIPMinimum.Variables.RestrictedVariables.cache_constraints___SERVER__REMOTE_ADDR__ error code has now also been changed.
  That is not to say that the change is incorrect, but it is a change the PR makes no mention of.

I will send in a PR shortly to fix the comments in the ruleset test case files for both changes.