Deprecate TaintedString (#15423)

Co-authored-by: Timothee Cour <timothee.cour2@gmail.com>
Co-authored-by: Dominik Picheta <dominikpicheta@googlemail.com>

doc/advopt.txt

@@ -93,7 +93,6 @@ Advanced options:
                             in the generated output
   --threadanalysis:on|off   turn thread analysis on|off
   --tlsEmulation:on|off     turn thread local storage emulation on|off
-  --taintMode:on|off        turn taint mode on|off
   --implicitStatic:on|off   turn implicit compile time evaluation on|off
   --trmacros:on|off         turn term rewriting macros on|off
   --multimethods:on|off     turn multi-methods on|off

doc/idetools.rst

@@ -329,7 +329,7 @@ skLet
     let
       text = "some text"
     --> col 2: $MODULE.text
-        col 3: TaintedString
+        col 3: string
         col 7: ""
 
 

doc/manual_experimental.rst

@@ -1718,28 +1718,6 @@ e.g. with given example ``echo("ab")`` will be rewritten just once:
 ``noRewrite`` pragma can be useful to control term-rewriting macros recursion.
 
 
-Taint mode
-==========
-
-The Nim compiler and most parts of the standard library support
-a taint mode. Input strings are declared with the `TaintedString`:idx:
-string type declared in the ``system`` module.
-
-If the taint mode is turned on (via the ``--taintMode:on`` command line
-option) it is a distinct string type which helps to detect input
-validation errors:
-
-.. code-block:: nim
-  echo "your name: "
-  var name: TaintedString = stdin.readline
-  # it is safe here to output the name without any input validation, so
-  # we simply convert `name` to string to make the compiler happy:
-  echo "hi, ", name.string
-
-If the taint mode is turned off, ``TaintedString`` is simply an alias for
-``string``.
-
-
 Aliasing restrictions in parameter passing
 ==========================================