Remove deprecated device context fields

[ueman]

There are a couple of fields which are deprecated in the device context. Those fields should be removed in v7.0. Follow up from #838

[philipphofmann]

@ueman, could you point out the deprecated fields in the description, please?

[ueman]

Here's the list:

device.language
device.timezone
device.screenResolution
device.theme

Speaking of removing deprecated fields, there are a couple more candidates:

• sentry-dart/dart/lib/src/enricher/io_enricher_event_processor.dart

  Lines 95 to 96 in 6ae0ef0

  	// should be moved to event.thread.name
  	if (isolate != null) 'isolate': isolate,

  since it was moved to event.thread.name and can be enabled by options.attachThreads
• This runtime key

  sentry-dart/dart/lib/src/enricher/io_enricher_event_processor.dart

  Line 58 in 6ae0ef0

  key: 'sentry_dart_runtime',

  since it doesn't add much value as name is already indicating what it is
• Same for this key

  sentry-dart/flutter/lib/src/flutter_enricher_event_processor.dart

  Line 224 in 6ae0ef0

  key: 'sentry_flutter_runtime',

  since it doesn't add much value as name is already indicating what it is

[ueman]

#934 introduced attaching http response data, so the MaxRequestBodySize and MaxResponseBodySize enums can be consolidated.