Remove special handling of mtail/node-exporter configs for old distros

roles/float-base/files/mtail.service

roles/float-base/files/mtail.service.buster

roles/float-base/files/mtail.service.stretch

roles/float-base/files/node-exporter.default

roles/float-base/files/node-exporter.default.buster

roles/float-base/files/node-exporter.default.stretch

roles/float-base/tasks/prometheus.yml

roles/float-base/tasks/syslog.yml