symantec_endpoint: use valid ECS values for fields

[efd6]

What does this PR do?

This cleans up items missed in the previous pass in #3244. Now verified by the tool's check.

Checklist

• I have reviewed tips for building integrations and this pull request is aligned with them.
• I have verified that all data streams collect metrics or logs.
• I have added an entry to my package's changelog.yml file.
• I have verified that Kibana version constraints are current according to guidelines.

Author's Checklist

• [ ]

How to test this PR locally

See #3016 (comment)

Related issues

• Closes symantec_endpoint using invalid field values according to ECS #3050

Screenshots

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• Start Time: 2022-05-11T12:31:49.933+0000

• Duration: 16 min 31 sec

Test stats 🧪

Test	Results
Failed	0
Passed	23
Skipped	0
Total	23

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🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	100.0% (1/1)	💚
Files	100.0% (1/1)	💚 3.589
Classes	100.0% (1/1)	💚 3.589
Methods	100.0% (19/19)	💚 11.716
Lines	98.914% (820/829)	👍 9.886
Conditionals	100.0% (0/0)	💚