Revert "[d3d11] Return error when mapping an already mapped image"

This reverts commit 1cc531e.

Even though an FFXIV apitrace clearly indicates that mapping an
already mapped subresource returns E_OUTOFMEMORY in that game,
this doesn't always seem to be correct behaviour.

Fixes #1148, #1149.

src/d3d11/d3d11_context_imm.cpp

@@ -340,9 +340,6 @@ namespace dxvk {
     if (unlikely(Subresource >= pResource->CountSubresources()))
       return E_INVALIDARG;
 
-    if (unlikely(pResource->GetMapType(Subresource) != D3D11_MAP(~0u)))
-      return E_OUTOFMEMORY;
-
     pResource->SetMapType(Subresource, MapType);
 
     VkFormat packedFormat = m_parent->LookupPackedFormat(