Remove Deprecated agentCollector and standaloneCollector configuration

[TylerHelmuth]

The agentCollector and standaloneCollector configuration sections in values.yaml were deprecated as part of the 0.14.0 release of the charts (#159). These sections should be removed from values.yaml and all references to them in the templates should be cleaned up. NOTES.txt should be updated to fail any install that attempts to use agentCollector or standaloneCollector.

This work should not be completed until the collector is at version 0.52.0 (current version is 0.50.0) to give time for existing users of the charts to switch to using mode.

Open question: should mode be defaulted to daemonset? Once agentCollector is removed, the charts will not be able to be installed with the default values.yaml unless we set a default value for mode.

[TylerHelmuth]

0.52.0 has been released. I will get started on this.