security/ca_root_nss: Rework port

• Use DISTVERSION directly instead of calling VERSION_NSS
• Make use of EXTRACT_AFTER_ARGS, reduces ~170Mbyte of I/O not used
• Remove ETCSYMLINK_CONFLICTS_INSTALL, no longer relevant
• Replace ${LN} -sf with ${RLN}
• Rearrange port Makefile to follow Porters Handbook more closely and to improve readability

PR: 295343
Reviewed by: fernape (previous iteration)
Approved by: maintainer timeout, 1+ month