Fix compatibility issues with Java 1.8 Map

Java 1.8 Map implements default methods - remove(K, V), which conflicts
with the remove(String, V) in gov.nist.core.MultiMapImp. This changes
deletes the method from the interface - gov.nist.core.MultiMap
as well as from the implementation in gov.nist.core.MultiMapImp as no
caller were found for the same.

Bug: 27426743
Change-Id: Ib19c608edcf5c866852bcc48cb18b40972f5e04c
3 files changed