security/zenmap: Update to 7.25 BETA2 and use security/nmap as MASTERDIR

security/nmap:

• Ensure MAINTAINER and COMMENT do not clobber those of slave port
• Add .if !defined(MASTERDIR) to prevent inclusion in slave port
• Do not include bsd.port.options.mk, as none of the features are used

security/zenmap:

• Convert to slave of security/nmap to ensure they are updated in lockstep
• Inherently update to 7.25 BETA2 (current version of security/nmap)
• Take maintainership
• Remove redundant port header variables included from MASTERDIR
• PKGNAME of zenmap achieved using PKGNAMEPREFIX=ze and PORTNAME=nmap
• Inherit LICENSE_FILE, as zenmap/COPYING states it is the same as nmap
• Set directory variables so they are not inhereted from MASTERDIR
• Convert post-extract to post-patch, as it is modifying WRKSRC files
• Fix REINPLACE command, as it was leaving the line with nothing but a single ',' and causing the build to fail
• Do not download external zenmap icon, as one is included in distfile

Approved by: ohauer (security/nmap maintainer), mat (mentor)
Differential Revision: https://reviews.freebsd.org/D7880