[3.13] Remove duplicate content in Mapping types - dict documentation (GH-141036) (#142809)

Co-authored-by: Owain Davies <116417456+OTheDev@users.noreply.github.com>

Author: miss-islington

Doc/library/stdtypes.rst

@@ -4854,9 +4854,6 @@ can be used interchangeably to index the same dictionary entry.
    being added is already present, the value from the keyword argument
    replaces the value from the positional argument.
 
-   Providing keyword arguments as in the first example only works for keys that
-   are valid Python identifiers.  Otherwise, any valid keys can be used.
-
    Dictionaries compare equal if and only if they have the same ``(key,
    value)`` pairs (regardless of ordering). Order comparisons ('<', '<=', '>=', '>') raise
    :exc:`TypeError`.  To illustrate dictionary creation and equality,