Deprecate TaintedString (#15423)

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

tests/stdlib/tmemlinesBuf.nim

@@ -5,7 +5,7 @@ disabled: "appveyor"
 
 import memfiles
 var inp = memfiles.open("tests/stdlib/tmemlinesBuf.nim")
-var buffer: TaintedString = ""
+var buffer: string = ""
 var lineCount = 0
 for line in lines(inp, buffer):
   lineCount += 1

tests/stdlib/tosproc.nim

@@ -195,15 +195,15 @@ else: # main driver
     # bugfix: windows stdin.close was a noop and led to blocking reads
     proc startProcessTest(command: string, options: set[ProcessOption] = {
                     poStdErrToStdOut, poUsePath}, input = ""): tuple[
-                    output: TaintedString,
+                    output: string,
                     exitCode: int] {.tags:
                     [ExecIOEffect, ReadIOEffect, RootEffect], gcsafe.} =
       var p = startProcess(command, options = options + {poEvalCommand})
       var outp = outputStream(p)
       if input.len > 0: inputStream(p).write(input)
       close inputStream(p)
-      result = (TaintedString"", -1)
-      var line = newStringOfCap(120).TaintedString
+      result = ("", -1)
+      var line = newStringOfCap(120)
       while true:
         if outp.readLine(line):
           result[0].string.add(line.string)
@@ -223,7 +223,7 @@ else: # main driver
     p.inputStream.flush()
     var line = ""
     var s: seq[string]
-    while p.outputStream.readLine(line.TaintedString):
+    while p.outputStream.readLine(line):
       s.add line
     doAssert s == @["10"]
 
@@ -235,15 +235,15 @@ else: # main driver
       deferScoped: p.close()
       do:
         var sout: seq[string]
-        while p.outputStream.readLine(x.TaintedString): sout.add x
+        while p.outputStream.readLine(x): sout.add x
         doAssert sout == @["start ta_out", "to stdout", "to stdout", "to stderr", "to stderr", "to stdout", "to stdout", "end ta_out"]
     block: # startProcess stderr (replaces old test `tstderr` + `ta_out`)
       var p = startProcess(output, dir, options={})
       deferScoped: p.close()
       do:
         var serr, sout: seq[string]
-        while p.errorStream.readLine(x.TaintedString): serr.add x
-        while p.outputStream.readLine(x.TaintedString): sout.add x
+        while p.errorStream.readLine(x): serr.add x
+        while p.outputStream.readLine(x): sout.add x
         doAssert serr == @["to stderr", "to stderr"]
         doAssert sout == @["start ta_out", "to stdout", "to stdout", "to stdout", "to stdout", "end ta_out"]