Kibana data/uuid file exists in the package of 7.6.0

[hubbleview]

Kibana version: 7.6.0

Elasticsearch version: 7.6.0

Original install method (e.g. download page, yum, from source, etc.):

• downloaded tar.gz package
• docker image

Describe the bug:
The Kibana 7.6.0 package includes the file data/uuid with content ce42b997-a913-4d58-be46-bb1937feedd6, which is not supposed to be there.

Checking on code, if uuid file doesn't exist, it will generate a new UUID for this kibana instance. However, as this file exists, all kibana instance will have the same UUID ce42b997-a913-4d58-be46-bb1937feedd6. In multiple Kibana instances environment, the Stack Monitoring will only show one Kibana instance.

Checked the package of prior version, like 7.5.2, 7.4.2, no such file there.

Steps to reproduce:

1. Download kibana 7.6.0 tar.gz package.
2. Unzip the tar.gz, run 2 kibana instances to connect to ES 7.6.0.
3. In Stack Monitoring page, there's only 1 Kibana instance in the list.

Expected behavior:
Delete data/uuid file in the package, let new Kibana instance generate UUID by itself.

[elasticmachine]

Pinging @elastic/kibana-operations (Team:Operations)

[elasticmachine]

Pinging @elastic/kibana-platform (Team:Platform)

[joshdover]

My current guess is that when the legacy optimizer runs to build the distributable it generates a UUID since it starts up Core.