Update SSVC schema JSON to ensure the top parent element is not part of a "definitions" as it causes issues when merging with CVE schema.

[sei-vsarvepalli]

Describe the bug
CVE schema would like to provide validation for the official version of the SSVC schema. This means they would like to use thier Node based tool to accept our schema. At this time, the Node tool does not offer a way to use #definitions to define the very root of the schema. Our current schema for uses such a definition - which we should update as seen in CVE JSON scheme Pull Request CVEProject/cve-schema#350

SSVC/data/schema/v1/Decision_Point_Value_Selection-1-0-1.schema.json

Line 100 in d118b86

"$ref": "#/definitions/SsvcdecisionpointgroupselectionSchema"

The new schema looks like

https://github.com/CVEProject/cve-schema/blob/1c08e97929e22b1983557fe6ea5a9573831d49db/schema/imports/ssvc/ssvc-v1.0.1.json

I will submit a signed PR to resolve this.