Completed normal subtask EXT-6621 (Code cleanup: Remove unused...

Completed normal subtask EXT-6621 (Code cleanup: Remove unused LLFloaterActiveSpeakers and related classes from viewer)

* Removed llfloateractivespeacker.h/cpp from CMakeLists.txt and from the repo.
* Removed llmediaremotectrl.h/cpp, llvoiceremotectrl.h/cpp from the repo (were not in CMakeLists.txt).
* Unused in 2.0 setings ("ShowVoiceChannelPopup" & "ShowVolumeSettingsPopup") are moved to the end of settings.xml (to not affect 1.23 if remove).
* Removed xml files related to Active Speakers floater and old Communication floater (related cpp files have been already removed). Also removed their localized versions.
* Also removed old textures related to removed xml and unused in 2.0 anymore.

Reviewed by Vadim at https://codereview.productengine.com/secondlife/r/226/

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branch : product-engine