ij-log-slf4j: remove slf4j-log4j binding deps

It is up to the consumer of the SLF4J logging module to add its own
preferred binding. Hardcoding the binding to log4j prevents such a
choice without using dependency exclusions.
ij-log-slf4j: use newer SLF4J and log4j version

This upgrades the versions to SLF4J 1.7.2 and log4j 1.2.17.