security/pks: the port had been further improved (+)

• Simplify Berkeley DB detection (rather than completely deleting the corresponding configure script section, assume that if user passes DBHDR she knows what she's doing and trust that value)
• Fix a harmless typo RSA_get0_p() -> DSA_get0_p() in the previous commit 6074b736dee1
• GC some more needless variables (MAKE_ENV, LDFLAGS) and enable IPv6 while I'm here