security/nmap: Update to 7.991 and rework port

• Remove obsolete mirror in MASTER_SITES
• Import upstream PR #3439 [1]
• Convert multiple variables from ?= to =
• Remove old historical references
• Remove .if !defined(MASTERDIR) definition
• Add libpcap from ports as a permanent dependency, also removes local patch for bundled version
• Update pcre2 dependency definition
• Sort USES
• Unbundle lua, also removes local patches for bundled version
• Don't extract unbundled libraries
• Remove MAKE_JOBS_UNSAFE
• Rename SSH2 to LIBSSH2 for consistency with tree
• Remove DOCS from OPTIONS_DEFAULT as framework always enables DOCS
• Simplify LibreSSL guard
• Follow Porters Handbook's example about stripping binaries in post-install section

1: https://github.com/nmap/nmap/pull/3439

PR: 297693
Reviewed by: cy (maintainer)