[8.14](backport #39028) x-pack/filebeat/module/salesforce: Remove dashboards

[mergify[bot]]

Description

This PR aims to remove dashboards from the recently revamped Salesforce module. The plan is to discontinue support for dashboards created in version 7.15.0, as the overall Beats framework has ceased support for version 8.X.X dashboards.

For the newer dashboards, support will continue in the upcoming revamp of the Salesforce Integration, ensuring that the latest features and functionalities are available for users.

Checklist

• [x] My code follows the style guidelines of this project
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] I have made corresponding change to the default configuration files
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

Related issues

• Relates https://github.com/elastic/obs-infraobs-team/issues/1277
• Relates https://github.com/elastic/obs-infraobs-team/issues/1248

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This is an automatic backport of pull request #39028 done by [Mergify](https://mergify.com).

[botelastic[bot]]

This pull request doesn't have a Team:<team> label.

[lalit-satapathy]

Since the BC builds of the 8.14 release needs to be closed, these removal of dashboards can be taken from 8.15 onwards. This PR should not be tied to 8.14 release.

[mergify[bot]]

This pull request has not been merged yet. Could you please review and merge it @kush-elastic? 🙏

[mergify[bot]]

This pull request has not been merged yet. Could you please review and merge it @kush-elastic? 🙏