Update docs for EvictionAttributes.getMaximum() no longer throwing UnsupportedOperationException for LRU Heap

TLDR: I think we can just document this updated change.   I didn't have much time to think about it earlier today but thinking about it now I can see why we changed this.  

Previously, the EvictionAttributes.getMaximum() used to throw an UnsupportedOperationException if the user tried to configure a Maximum on an LRU Heap Eviction Policy (Apache Geode 1.4).  Now Geode (and by extension, GemFire) will just silently return 0.

IF this change is intentional the docs should be updated accordingly.   

http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/EvictionAttributes.html#getMaximum--

in 1.4

https://github.com/apache/geode/blob/rel/v1.4.0/geode-core/src/main/java/org/apache/geode/internal/cache/EvictionAttributesImpl.java#L138-L144

in 1.5

https://github.com/apache/geode/blob/rel/v1.5.0/geode-core/src/main/java/org/apache/geode/internal/cache/EvictionAttributesImpl.java#L95-L101