Clean up test function pk_parse_key

- remove incorrect compile-time dependency (the individual cases already have
  correct run-time dependency information)
- remove unused argument
- remove unused stack buffer
- remove useless code block
diff --git a/tests/suites/test_suite_pkparse.data b/tests/suites/test_suite_pkparse.data
index fc643a8..328f3e0 100644
--- a/tests/suites/test_suite_pkparse.data
+++ b/tests/suites/test_suite_pkparse.data
@@ -1073,32 +1073,32 @@
 pk_parse_keyfile_ec:"data_files/ec_prv.specdom.der":"NULL":0
 
 Key ASN1 (Incorrect first tag)
-pk_parse_key:"":"":MBEDTLS_ERR_PK_KEY_INVALID_FORMAT
+pk_parse_key:"":MBEDTLS_ERR_PK_KEY_INVALID_FORMAT
 
 Key ASN1 (RSAPrivateKey, incorrect version tag)
 depends_on:MBEDTLS_RSA_C
-pk_parse_key:"300100":"":MBEDTLS_ERR_PK_KEY_INVALID_FORMAT
+pk_parse_key:"300100":MBEDTLS_ERR_PK_KEY_INVALID_FORMAT
 
 Key ASN1 (RSAPrivateKey, version tag missing)
 depends_on:MBEDTLS_RSA_C
-pk_parse_key:"3000":"":MBEDTLS_ERR_PK_KEY_INVALID_FORMAT
+pk_parse_key:"3000":MBEDTLS_ERR_PK_KEY_INVALID_FORMAT
 
 Key ASN1 (RSAPrivateKey, invalid version)
 depends_on:MBEDTLS_RSA_C
-pk_parse_key:"3003020101":"":MBEDTLS_ERR_PK_KEY_INVALID_FORMAT
+pk_parse_key:"3003020101":MBEDTLS_ERR_PK_KEY_INVALID_FORMAT
 
 Key ASN1 (RSAPrivateKey, correct version, incorrect tag)
 depends_on:MBEDTLS_RSA_C
-pk_parse_key:"300402010000":"":MBEDTLS_ERR_PK_KEY_INVALID_FORMAT
+pk_parse_key:"300402010000":MBEDTLS_ERR_PK_KEY_INVALID_FORMAT
 
 Key ASN1 (RSAPrivateKey, values present, length mismatch)
 depends_on:MBEDTLS_RSA_C
-pk_parse_key:"301c02010002010102010102010102010102010102010102010102010100":"":MBEDTLS_ERR_PK_KEY_INVALID_FORMAT
+pk_parse_key:"301c02010002010102010102010102010102010102010102010102010100":MBEDTLS_ERR_PK_KEY_INVALID_FORMAT
 
 Key ASN1 (RSAPrivateKey, values present, check_privkey fails)
 depends_on:MBEDTLS_RSA_C
-pk_parse_key:"301b020100020102020101020101020101020101020101020101020101":"":MBEDTLS_ERR_PK_KEY_INVALID_FORMAT
+pk_parse_key:"301b020100020102020101020101020101020101020101020101020101":MBEDTLS_ERR_PK_KEY_INVALID_FORMAT
 
 Key ASN1 (ECPrivateKey, empty parameters)
 depends_on:MBEDTLS_ECP_C
-pk_parse_key:"30070201010400a000":"":MBEDTLS_ERR_PK_KEY_INVALID_FORMAT
+pk_parse_key:"30070201010400a000":MBEDTLS_ERR_PK_KEY_INVALID_FORMAT