Remove the CrowdSec decision feed (closes #315)

sneak ruled to remove it. Gone: the heuristic crowdsec, the ban cause
crowdsec and its earlier_bans count, the tag crowdsec, the settings
SWW_WAF_CROWDSEC_LAPI_URL and SWW_WAF_CROWDSEC_LAPI_KEY, the decision
list fetch and parse in internal/reputation, their tests, and every
mention in the README, SPEC.md and docs/. EVALUATION.md keeps its
comparison of tools.

The ban ledger's internal ban function loses its expires parameter,
which only CrowdSec bans used.

Model: opus-5-5

internal/waf/bans.go

@@ -11,7 +11,6 @@ import (
 	"sneak.berlin/go/smallwebwaf/internal/alerts"
 	"sneak.berlin/go/smallwebwaf/internal/bans"
 	"sneak.berlin/go/smallwebwaf/internal/ratelimit"
-	"sneak.berlin/go/smallwebwaf/internal/reputation"
 	"sneak.berlin/go/smallwebwaf/internal/requestlog"
 )
 
@@ -206,57 +205,6 @@ func (rq *request) banForAttack(now time.Time, notes bans.Notes) string {
 	return banAction(ban.Permanent())
 }
 
-// banForCrowdSec bans the client's netblock at now until decision,
-// CrowdSec's decision on the client, ends. In observe mode it makes no
-// ban, and raises the alert for the ban it would have made, if that alert
-// would be sent. It returns the action for that ban.
-func (rq *request) banForCrowdSec(
-	now time.Time,
-	decision reputation.Decision,
-) string {
-	netblock := rq.h.netblock(rq.client)
-	if rq.h.config.Observe &&
-		!rq.wouldAlertBan(netblock, now, bans.CauseCrowdSec) {
-		return banAction(
-			rq.h.ledger.WouldBePermanent(netblock, now, bans.CauseCrowdSec),
-		)
-	}
-
-	notes := bans.Notes{
-		ASN:        rq.line.ASN,
-		ASName:     rq.line.ASName,
-		Country:    rq.line.Country,
-		Reputation: rq.reputation,
-		Request:    rq.noted(now, rq.h.config.BanResponse),
-		Requests:   rq.netblockRequests(netblock),
-	}
-
-	if rq.h.config.Observe {
-		ban, wouldBan := rq.h.ledger.WouldBanForCrowdSec(
-			netblock,
-			now,
-			decision.Expires,
-			decision.Scenario,
-			notes,
-		)
-		if wouldBan {
-			rq.alertBan(ban)
-		}
-
-		return banAction(ban.Permanent())
-	}
-
-	ban, made := rq.h.ledger.BanForCrowdSec(netblock, now, decision.Expires,
-		decision.Scenario, notes)
-	rq.line.BanExpires = banExpires(ban)
-
-	if made {
-		rq.alertBan(ban)
-	}
-
-	return banAction(ban.Permanent())
-}
-
 // wouldAlertBan reports whether the alert for a ban on netblock for cause
 // made at now would be sent. In observe mode the ban the request would
 // have made is worked out only then, at most once per