Ensure metric embed store is not initialized on every page

What does this MR do?

Removes the Metric Embed Vuex store initialization from every page that has gfm.

This saves some (minimal) script processing and more importantly de-clutters the VueJS dev tools, since they were loading the embed store into the vuex tab on nearly every page.

There is no functional change to the application, the deleted code was not used.

Fixes #322829 (closed)

Screenshots (strongly suggested)

before (two stores in vuex tools)	after (one store in vuex tools)

Does this MR meet the acceptance criteria?

Conformity

• [n/a] Changelog entry
• [n/a] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [n/a] Database guides
• [n/a] Separation of EE specific content

Availability and Testing

• [n/a] Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• [n/a] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

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

Related to #322829 (closed)