Removed the http4client.retain_max_body_size property mentions

[kkalinin]

Description

I've removed the http4client.retain_max_body_size property mentions from documentation and jmeter.properties file.

Motivation and Context

The property is not used anymore and just confuses users.

How Has This Been Tested?

No need to test, only text files modified`

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code follows the [code style][style-guide] of this project.
• I have updated the documentation accordingly.

[vlsi]

@pmouawad , I see the property was removed in 97cc6f4
Do you think it should be completely removed or should it be re-implemented somehow?

[pmouawad]

@pmouawad , I see the property was removed in 97cc6f4
Do you think it should be completely removed or should it be re-implemented somehow?

I would prefer to have it re-implemented somehow