Remove deprecated config options for RUM

[simitt]

In 7.15 several RUM related configuration options have been deprecated. Since they were deprecated throughout the whole 8.x lifecycle, they should be removed in 9.0. All of the removed config options have a replacement available, so we are not taking away functionality. The goal is to have more streamlined configuration options.

The following options should be removed:

• apm-server.rum.event_rate.limit
• apm-server.rum.event_rate.lru_size
• apm-server.rum.allow_service_names

Deprecation has been documented.