[docs] [issue18572] Remove redundant note about surrogates in string escape doc

[Terry J. Reedy]

Changes by Terry J. Reedy <tjreedy at udel.edu>:


----------
stage:  -> needs patch
type:  -> behavior
versions: +Python 3.4

_______________________________________
Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue18572>
_______________________________________