Change mrcp_server to not store handler on registrar

[MayamaTakeshi]

In the current code, when mrcp_server gets SESSION_CREATED, it instantiates a resource handler and stores it in the call in the registrar.
However, reading:
https://nact.io/en_uk/lesson/javascript/hierarchy
this is not necessary:
we just need to create the resource handler passing the uuid as its name and when an MRCP message with that uuid arrives we can check if there is a children using that name and if yes, relay the message to it.

[MayamaTakeshi]

I tried to do this change. but ctx.children.has(uuid) is returning false when the handler exists as child of mrcp_server:

new handler
ActorReference {
  path: ActorPath {
    system: 'cnkqt9-169c4g8-1l3rilx-1cwbn3x',
    parts: [ 'mrcp_server', 'cf148e7a-6eda-4077-930f-10d2a3fdbdc9' ]
  },
  name: 'cf148e7a-6eda-4077-930f-10d2a3fdbdc9',
  parent: ActorReference {
    path: ActorPath {
      system: 'cnkqt9-169c4g8-1l3rilx-1cwbn3x',
      parts: [Array]
    },
    name: 'mrcp_server',
    parent: ActorSystemReference {
      path: [ActorPath],
      system: [Object],
      name: 'cnkqt9-169c4g8-1l3rilx-1cwbn3x',
      type: 'system'
    },
    system: { name: 'cnkqt9-169c4g8-1l3rilx-1cwbn3x' },
    type: 'actor'
  },
  system: { name: 'cnkqt9-169c4g8-1l3rilx-1cwbn3x' },
  type: 'actor'
}
2021-02-14 12:13:09.915 error: cf148e7a-6eda-4077-930f-10d2a3fdbdc9 (mrcp_server.js:86) setting handler for speechsynth
2021-02-14 12:13:09.915 info: cf148e7a-6eda-4077-930f-10d2a3fdbdc9 (mrcp_server.js:91) sending SESSION_CREATED_ACK to {"path":{"system":"cnkqt9-169c4g8-1l3rilx-1cwbn3x","parts":["sip_server"]},"name":"sip_server
","parent":{"path":{"system":"cnkqt9-169c4g8-1l3rilx-1cwbn3x","parts":[]},"system":{"name":"cnkqt9-169c4g8-1l3rilx-1cwbn3x"},"name":"cnkqt9-169c4g8-1l3rilx-1cwbn3x","type":"system"},"system":{"name":"cnkqt9-169c
4g8-1l3rilx-1cwbn3x"},"type":"actor"}
2021-02-14 12:13:09.916 info: cf148e7a-6eda-4077-930f-10d2a3fdbdc9 (speechsynther.js:28) got START
2021-02-14 12:13:09.916 info: sip_server (sip_server.js:212) got SESSION_CREATED_ACK
2021-02-14 12:13:09.916 info: cf148e7a-6eda-4077-930f-10d2a3fdbdc9 (sip_server.js:314) INVITE for speechsynth accepted with 200 OK
2021-02-14 12:13:09.921 info: cf148e7a-6eda-4077-930f-10d2a3fdbdc9 (sip_server.js:162) got SIP request ACK
2021-02-14 12:13:09.923 warning: cf148e7a-6eda-4077-930f-10d2a3fdbdc9 (mrcp_server.js:45) got unexpected MRCP message {"type":"request","version":"2.0","method":"SPEAK","request_id":1,"headers":{"channel-identif
ier":"cf148e7a-6eda-4077-930f-10d2a3fdbdc9@speechsynth","content-type":"text/plain","speech-language":"dtmf","voice-name":"dtmf","content-length":"16"},"body":"1234567890abcd*#","uuid":"cf148e7a-6eda-4077-930f-1
0d2a3fdbdc9"} for unknown uuid=cf148e7a-6eda-4077-930f-10d2a3fdbdc9

So I will put this on hold.