Removes legacy pipelines code from kibana core_plugin

[BigFunger]

Closes #9320

Removes legacy Pipelines code from core kibana

[ycombinator]

I checked out this PR and clicked around the UI to make sure nothing broke. Nothing broke :)

LGTM.

[ycombinator]

jenkins, test this.

[ycombinator]

@BigFunger Any ideas why the CI is failing this test?

>> FAIL: ingest API - simulate - should return 400 for an invalid payload (55ms)
Error: expected 400 "Bad Request", got 404 "Not Found"
  at Test._assertStatus  <node_modules/supertest/lib/test.js:232:12>
  at Test._assertFunction  <node_modules/supertest/lib/test.js:247:11>
  at Test.assert  <node_modules/supertest/lib/test.js:148:18>
  at assert  <node_modules/supertest/lib/test.js:127:12>
  at <node_modules/supertest/lib/test.js:124:5>
  at Test.Request.callback  <node_modules/superagent/lib/node/index.js:703:3>
  at Stream.<anonymous>  <node_modules/superagent/lib/node/index.js:922:12>
  at emitNone  <events.js:91:20>
  at Stream.emit  <events.js:185:7>
  at Unzip.<anonymous>  <node_modules/superagent/lib/node/utils.js:108:12>
  at emitNone  <events.js:91:20>
  at Unzip.emit  <events.js:185:7>
  at endReadableNT  <_stream_readable.js:974:12>
  at _combinedTickCallback  <internal/process/next_tick.js:74:11>
  at process._tickCallback  <internal/process/next_tick.js:98:9>

[w33ble]

Gave this a go, everything still looks like it works. There's a bunch of ingest tests that I think you need to remove, but otherwise, this looks fine.