fixes #8916 by fixing typeinfo and marshal. (#9341)

* fixes #8916 by removing `tyString`, `tySeq`, mod. marshal, typeinfo

Need to check in `typeinfo` for nil of the underlying pointer.
In marshal don't have to check for nil of seq anymore.

* remove reference to string, sequence in `isNil` doc string

lib/pure/marshal.nim

@@ -54,13 +54,11 @@ proc storeAny(s: Stream, a: Any, stored: var IntSet) =
     else:
       s.write($int(ch))
   of akArray, akSequence:
-    if a.kind == akSequence and isNil(a): s.write("null")
-    else:
-      s.write("[")
-      for i in 0 .. a.len-1:
-        if i > 0: s.write(", ")
-        storeAny(s, a[i], stored)
-      s.write("]")
+    s.write("[")
+    for i in 0 .. a.len-1:
+      if i > 0: s.write(", ")
+      storeAny(s, a[i], stored)
+    s.write("]")
   of akObject, akTuple:
     s.write("{")
     var i = 0