crypto/hpke: remove unused hybridKEM field

hybridKEM.pqGenerateKey is not used anywhere. Having it around
is confusing, as it suggests that the mlkem seed is generated within
the mlkem package, when it is not.

Change-Id: Ie0bdb79d6b774db7b21dfff2b966452463f1ce08
Reviewed-on: https://go-review.googlesource.com/c/go/+/726260
Reviewed-by: Filippo Valsorda <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
Reviewed-by: Roland Shoemaker <[email protected]>

Author: qmuntal

src/crypto/hpke/pq.go

@@ -33,9 +33,6 @@ var mlkem768X25519 = &hybridKEM{
 	pqNewPrivateKey: func(data []byte) (crypto.Decapsulator, error) {
 		return mlkem.NewDecapsulationKey768(data)
 	},
-	pqGenerateKey: func() (crypto.Decapsulator, error) {
-		return mlkem.GenerateKey768()
-	},
 }
 
 // MLKEM768X25519 returns a KEM implementing MLKEM768-X25519 (a.k.a. X-Wing)
@@ -60,9 +57,6 @@ var mlkem768P256 = &hybridKEM{
 	pqNewPrivateKey: func(data []byte) (crypto.Decapsulator, error) {
 		return mlkem.NewDecapsulationKey768(data)
 	},
-	pqGenerateKey: func() (crypto.Decapsulator, error) {
-		return mlkem.GenerateKey768()
-	},
 }
 
 // MLKEM768P256 returns a KEM implementing MLKEM768-P256 from draft-ietf-hpke-pq.
@@ -86,9 +80,6 @@ var mlkem1024P384 = &hybridKEM{
 	pqNewPrivateKey: func(data []byte) (crypto.Decapsulator, error) {
 		return mlkem.NewDecapsulationKey1024(data)
 	},
-	pqGenerateKey: func() (crypto.Decapsulator, error) {
-		return mlkem.GenerateKey1024()
-	},
 }
 
 // MLKEM1024P384 returns a KEM implementing MLKEM1024-P384 from draft-ietf-hpke-pq.
@@ -108,7 +99,6 @@ type hybridKEM struct {
 
 	pqNewPublicKey  func(data []byte) (crypto.Encapsulator, error)
 	pqNewPrivateKey func(data []byte) (crypto.Decapsulator, error)
-	pqGenerateKey   func() (crypto.Decapsulator, error)
 }
 
 func (kem *hybridKEM) ID() uint16 {