Revert "follow #16009 VM supports cast nil to ptr (#16012)"

This reverts commit fec19c980e.

compiler/vmgen.nim

@@ -901,9 +901,6 @@ proc genCastIntFloat(c: PCtx; n: PNode; dest: var TDest) =
     c.gABx(n, opcSetType, dest, c.genType(dst))
     c.gABC(n, opcCastIntToPtr, dest, tmp)
     c.freeTemp(tmp)
-  elif src.kind == tyNil and dst.kind in PtrLikeKinds:
-    if dest < 0: dest = c.getTemp(n[0].typ)
-    genLit(c, n[1], dest)
   else:
     # todo: support cast from tyInt to tyRef
     globalError(c.config, n.info, "VM does not support 'cast' from " & $src.kind & " to " & $dst.kind)

tests/vm/tcastnil.nim

@@ -1,30 +0,0 @@
-discard """
-  nimout: '''nil
-nil
-nil
-nil
-nil
-'''
-"""
-
-block:
-  static:
-    let a = cast[pointer](nil)
-    echo a.repr
-
-block:
-  static:
-    echo cast[ptr int](nil).repr
-
-block:
-  const str = cast[ptr int](nil)
-  static:
-    echo str.repr
-
-block:
-  static:
-    echo cast[ptr int](nil).repr
-
-block:
-  static:
-    echo cast[RootRef](nil).repr