CLEANUP: quic: remove unused QUIC_LOCK label

QUIC_LOCK label is never used. Indeed, lock usage is minimal on QUIC as
every connection is pinned to its owned thread.

This should be backported up to 2.7.
diff --git a/include/haproxy/thread.h b/include/haproxy/thread.h
index 67ceba3..b504ab6 100644
--- a/include/haproxy/thread.h
+++ b/include/haproxy/thread.h
@@ -423,7 +423,6 @@
 	SSL_SERVER_LOCK,
 	SFT_LOCK, /* sink forward target */
 	IDLE_CONNS_LOCK,
-	QUIC_LOCK,
 	OCSP_LOCK,
 	OTHER_LOCK,
 	/* WT: make sure never to use these ones outside of development,
diff --git a/src/thread.c b/src/thread.c
index 84d39d7..6001f8c 100644
--- a/src/thread.c
+++ b/src/thread.c
@@ -442,7 +442,6 @@
 	case SSL_SERVER_LOCK:      return "SSL_SERVER";
 	case SFT_LOCK:             return "SFT";
 	case IDLE_CONNS_LOCK:      return "IDLE_CONNS";
-	case QUIC_LOCK:            return "QUIC";
 	case OCSP_LOCK:            return "OCSP";
 	case OTHER_LOCK:           return "OTHER";
 	case DEBUG1_LOCK:          return "DEBUG1";