This commit aligns our dependency management for GemFire with the
version used by the version of Spring Data GemFire that we currently
depend upon.

Previously, some dependency management that was added (see #2884) to
work around problems with GemFire 8.0’s dependencies; specifically it
depended on different versions of org.eclipse.jdt.core.compiler:ecj and
xml-apis:xml-apis. The different dependency versions appear to no
longer be a problem with 8.1 so this dependency management is now
redundant and has been removed.

Closes gh-3284