docs: remove RFC key words

since the page is not an specification in RFC terms.

docs/source/specification.rst

 Simple Bandwidth Scanner technical details
 ============================================
 
-Conventions
------------
-
-The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD",
-"SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL"
-in this document are to be interpreted as described in BCP 14 (:rfc:`2119`
-and :rfc:`8174`) when, and only when, they appear in all capitals, as shown
-here.
-
 Background
 ----------