autotools: Don't regenerate Wycheproof header automatically

Pregenerated files that we distribute should not have dependencies
in Makefile.am. For rationale, see the comments about the precomputed
table files.

See also bitcoin#27445 (comment) .

Makefile.am

@@ -255,8 +255,8 @@ EXTRA_DIST += tools/tests_wycheproof_generate.py
 
 TESTVECTORS = src/wycheproof/ecdsa_secp256k1_sha256_bitcoin_test.h
 
-src/wycheproof/ecdsa_secp256k1_sha256_bitcoin_test.h: src/wycheproof/ecdsa_secp256k1_sha256_bitcoin_test.json
-	python3 tools/tests_wycheproof_generate.py $< > $@
+src/wycheproof/ecdsa_secp256k1_sha256_bitcoin_test.h:
+	python3 tools/tests_wycheproof_generate.py src/wycheproof/ecdsa_secp256k1_sha256_bitcoin_test.json > $@
 
 testvectors: $(TESTVECTORS)