Remove dataBackground property from chart

What does this MR do?

This commit removes the dataBackground property from the chart options so that it behaves similar to the other charts on GitLab.

Especially when gitlab-ui!2185 (merged) will be merged, the chart looks much different due to the breaking changes. In order to avoid that, I've created this MR beforehand.

Screenshots or Screencasts (strongly suggested)

Today	With Echarts 5	After

How to setup and validate locally (strongly suggested)

You'll need to have the Security Dashboard enabled to view this chart. This is an EE feature, so you'll also need a license. Here are the steps to produce vulnerabilities locally:

1. Clone https://gitlab.com/gitlab-examples/security/security-reports/
2. Run the pipeline by going into Your project > CI/CD > Pipelines
3. Click on run pipeline for master branch

It should generate the list. You should have the runner installed in order to run this.

Then using the following command you can register the runner, it guides you pretty good:

$ gitlab-runner register

Once it's installed this is how I run the runner:

$ gitlab-runner --log-level debug run local-runner --config ~/.gitlab-runner/config.toml restart

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.
• I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.

Security

Does this MR contain changes to processing or storing of credentials or tokens, authorization and authentication methods or other items described in the security review guidelines? If not, then delete this Security section.

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team