[httpjson] Remove defaults from manifest.

[marc-gr]

What does this PR do?

Template breaks when yaml contents are all comments under some circumstances. The default examples were causing some issues because of that for some configurations.

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.

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Pinging @elastic/security-external-integrations (Team:Security-External Integrations)

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• Start Time: 2022-07-07T08:57:09.395+0000

• Duration: 17 min 57 sec

Test stats 🧪

Test	Results
Failed	0
Passed	7
Skipped	0
Total	7

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🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	100.0% (0/0)	💚
Files	100.0% (0/0)	💚 3.171
Classes	100.0% (0/0)	💚 3.171
Methods	100.0% (3/3)	💚 10.445
Lines	100.0% (0/0)	💚 8.916
Conditionals	100.0% (0/0)	💚