net-mgmt/cacti: Update to 1.2.5

• Remove the SNMPBIN option that was introduced with r490477 and which is no longer required since the 1.2.4 release.
  
  It was used as a workaround to override the internal PHP SNMP calls which led to graphs that didn't update within cacti.
  
  The PHP SNMP extension can now be enabled/disabled by a re-purposed variable in the configuration file.

While I'm here:

• Remove superfluous "+=" from PLIST_SUB and SUB_LIST because there are no previous definitions of those variables.

• Remove CONFLICTS_INSTALL as net-mgmt/cacti88 is no longer present in the Ports tree since the end of 2018.

Changes since 1.2.3:

https://github.com/Cacti/cacti/blob/release/1.2.5/CHANGELOG

PR: 238434
Submitted by: Michael Muenz <m.muenz@gmail.com>
Reported by: Matthew Horan <matt@matthoran.com>
Approved by: maintainer timeout (2+ months)
MFH: 2019Q3