Stop overriding logging.{ecs,json} defaults

[axw]

Motivation/summary

Stop overriding the defaults for logging.ecs and logging.json. These are now both forced on by libbeat (elastic/beats#28573).

Checklist

• Update CHANGELOG.asciidoc
  - [ ] Documentation has been updated (Relevant docs are copied from beats.)

How to test these changes

1. Run apm-server -e
2. Check logs are ECS+JSON

Related issues

elastic/beats#28573

[apmmachine]

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Build stats

• Start Time: 2021-11-15T10:41:56.281+0000

• Duration: 51 min 55 sec

• Commit: 387aab3

Test stats 🧪

Test	Results
Failed	0
Passed	6014
Skipped	19
Total	6033

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[marclop]

Verified with 9bb5e4c.

$ /apm-server -E output.elasticsearch.username=admin -E output.elasticsearch.password=changeme -E apm-server.rum.enabled= -e
{"log.level":"info","@timestamp":"2021-12-21T14:59:13.371+0800","log.logger":"beater","log.origin":{"file.name":"beater/http.go","file.line":88},"message":"RUM endpoints enabled!","service.name":"apm-server","ecs.version":"1.6.0"}
{"log.level":"warn","@timestamp":"2021-12-21T14:59:13.372+0800","log.logger":"beater","log.origin":{"file.name":"beater/http.go","file.line":91},"message":"CORS related setting `apm-server.rum.allow_origins` allows all origins. Consider more restrictive setting for production use.","service.name":"apm-server","ecs.version":"1.6.0"}
{"log.level":"info","@timestamp":"2021-12-21T14:59:13.372+0800","log.logger":"beater","log.origin":{"file.name":"beater/http.go","file.line":106},"message":"SSL disabled.","service.name":"apm-server","ecs.version":"1.6.0"}

{"log.level":"error","@timestamp":"2021-12-21T14:59:20.093+0800","log.logger":"request","log.origin":{"file.name":"middleware/log_middleware.go","file.line":58},"message":"data validation error","service.name":"apm-server","url.original":"/intake/v2/rum/events","http.request.method":"POST","user_agent.original":"curl/7.64.1","source.address":"127.0.0.1","http.request.body.bytes":0,"http.request.id":"7fafc293-b89f-459f-abf8-eda4d2a9318b","event.duration":1088584,"http.response.status_code":400,"error.message":"validation error: 'metadata' required","ecs.version":"1.6.0"}
{"log.level":"info","@timestamp":"2021-12-21T14:59:49.907+0800","log.logger":"request","log.origin":{"file.name":"middleware/log_middleware.go","file.line":61},"message":"request accepted","service.name":"apm-server","url.original":"/intake/v2/rum/events","http.request.method":"POST","user_agent.original":"curl/7.64.1","source.address":"127.0.0.1","http.request.body.bytes":1096,"http.request.id":"5da04119-499d-47a6-8355-0534207f98af","event.duration":52282167,"http.response.status_code":202,"ecs.version":"1.6.0"}
{"log.level":"info","@timestamp":"2021-12-21T15:08:06.904+0800","log.logger":"request","log.origin":{"file.name":"middleware/log_middleware.go","file.line":61},"message":"request accepted","service.name":"apm-server","url.original":"/intake/v2/events","http.request.method":"POST","user_agent.original":"curl/7.64.1","source.address":"127.0.0.1","http.request.body.bytes":4700,"http.request.id":"c281207d-1e2d-4229-87a5-c03c39f07716","event.duration":2648916,"http.response.status_code":202,"ecs.version":"1.6.0"}