docs: Remove space-before-label guidance from CodingStyle

Recent discussion has made it clear that there is no community consensus on
this particular rule.  Remove it now, lest it inspire yet another set of
unwanted "cleanup" patches.

This partially reverts 865a1caa (CodingStyle: Clarify and complete
chapter 7).

Cc: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>