remove redundancy

draft-ietf-quic-tls.md

@@ -1165,14 +1165,12 @@ another key update can be initiated.
 Endpoints MAY limit the number of keys they retain to two sets for removing
 packet protection.
 
-An endpoint installs the new keys, possibly replacing the old keys, when it
-unprotects the header protection of a received packet and detects that the
-packet uses a new key phase.  The detection can be done by tracking the lowest
-packet number among the packets received with the currently active key phase.
-If a packet is received that has a different KEY_PHASE bit and a lower packet
-number than this value, the endpoint uses the old keys for unprotecting the
-packet, if these keys are still available.  If the packet has a higher packet
-number, the endpoint installs the updated keys.
+An endpoint can detect which keys to use by tracking the lowest packet number
+among the packets received with the currently active key phase.  If a packet is
+received that has a different KEY_PHASE bit and a lower packet number than this
+value, the endpoint uses the old keys for unprotecting the packet, if these keys
+are still available.  If the packet has a higher packet number, the endpoint
+installs the updated keys.
 
 Updating keys multiple times rapidly can cause packets to be effectively lost if
 packets are significantly reordered.  Therefore, an endpoint SHOULD NOT initiate