[Ingest Manager] Clean action store after enrolling to new configuration

[michalpristas]

What does this PR do?

Removes an action_store file after agent enrolls to a new config.

Why is it important?

Gets rid of error messages which are related to old configuration and wont go away

Checklist

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

Fixes: #17389

[elasticmachine]

Pinging @elastic/ingest-management (Team:Ingest Management)

[elasticmachine]

💚 Build Succeeded

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Build stats

• Build Cause: [Pull request [Ingest Manager] Clean action store after enrolling to new configuration #18656 updated]

• Start Time: 2020-05-20T09:41:11.174+0000

• Duration: 30 min 14 sec (1814335)

Test stats 🧪

Test	Results
Failed	0
Passed	497
Skipped	127
Total	624

[EricDavisX]

love this, thanks Michal. @ph @michalpristas you thinking to do the 7.8 backport as well? just checking.

[ph]

I think we should this is low risk.

[michalpristas]

will abackport to both