rm useless generics for DensePolynomial (#903) #3228

Job	Run time
Check Style	9s
Check (nightly)	1m 9s
Check (stable)	14s
Test (nightly)	17m 40s
Check Documentation	57s
Test assembly	8m 24s
Test (mnt4_753/)	12m 32s
Test (cp6_782/)	6s
Test (stable)	8m 58s
Test (mnt6_753/)	13s
List directories for parallelizing tests	4s
Check no_std	25s
Test (./ed_on_bn254)	1m 5s
Test (./mnt4_298)	3m 54s
Test (./vesta)	1m 9s
Test (./ed_on_bls12_381)	1m 9s
Test (./curve25519)	1m 4s
Test (./bls12_381)	3m 7s
Test (./ed_on_bw6_761)	39s
Test (./ed_on_mnt4_753)	3m 44s
Test (./ed_on_bls12_381_bandersnatch)	1m 3s
Test (./pallas)	1m 18s
Test (./grumpkin)	1m 7s
Test (./ed_on_cp6_782)	1m 17s
Test (./secp256r1)	1m 3s
Test (./secp256k1)	1m 3s
Test (./bn254)	2m 13s
Test (./secq256k1)	59s
Test (./bw6_767)	3m 48s
Test (./secp384r1)	1m 18s
Test (./ed_on_mnt4_298)	1m 23s
Test (./ed25519)	59s
Test (./ed_on_bls12_377)	1m 8s
Test (./bls12_377)	3m 56s
Test (./bw6_761)	3m 45s
Test (./mnt6_298)	4m 48s
	1h 37m 50s

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