Customisable-Sniff-Properties: remove PSR12/OperatorSpacing sniff section

[jrfnl]

Description

As per the inline comment replacing the section:

While PSR12.Operators.OperatorSpacing inherits the ignoreNewlines and ignoreSpacingBeforeAssignments properties
from the Squiz.WhiteSpace.OperatorSpacing sniff, these properties are not handled in the PSR12 sniff,
so are deliberately not mentioned in this documentation.

Related issues/external references

Discovered while reviewing upstream PR PHPCSStandards/PHP_CodeSniffer#1356

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[github-actions]

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