drop most usage of Guava's com.google.common package

[maggu2810]

This drops the most usage of com.google.common.

The model bundle has been kept untouched as Xtext itself needs Guava and generates code that uses it.

The other remaining usages (all can be done in another PR and should not block this cleanup):

bundle (esh)	class	Guava (collect)	note
io.rest.sitemap	SitemapResource.java	MapMaker	It uses some weak reference related stuff. @kaikreuzer AFAIK this has been introduced by you. Correct? Can you come up with some other suggestion?
config.discovery	DiscoveryServiceRegistryImpl	HashMultimap
core.thing	ThingManagerImpl	HashMultimap
core.thing	ThingManagerImpl	Multimaps
core.thing	ThingManagerImpl	SetMultimap

[kaikreuzer]

Can you come up with some other suggestion?

The MapMaker is pretty convenient, so not completely easy to replace it. Asking SO, https://stackoverflow.com/a/33703220 might be the best alternative, wdyt?

[maggu2810]

https://commons.apache.org/proper/commons-collections/apidocs/org/apache/commons/collections4/map/ReferenceMap.html

Also available on v3:
https://commons.apache.org/proper/commons-collections/javadocs/api-3.2.2/org/apache/commons/collections/ReferenceMap.html

[htreu]

LGTM. I suggest merging this and postpone the replacement of MapMaker to a separate PR. I will create an issue for follow up.

[maggu2810]

I suggest merging this and postpone the replacement of MapMaker to a separate PR

Me, too

The other remaining usages (all can be done in another PR and should not block this cleanup):

[htreu]

Replace MapMaker issue: #6460