[d3d8] Remove references to d3d8.useShadowBuffers for now

The current D3D8 codebase in DXVK does not implement this
feature, i.e. setting this option is a NOP. It was
implemented in D8VK at some point, but was removed before
the big merge.

Remove any references to avoid confusion.

dxvk.conf

@@ -709,16 +709,3 @@
 # - True/False
 
 # d3d9.countLosableResources = True
-
-# Use NVIDIA Shadow Buffers
-# 
-# Vendor behavior for GeForce3 and GeForce4 cards that allows
-# sampling depth textures with non-normalized Z coordinates
-# and applies hardware shadow filtering.
-#
-# Supported values:
-# - True/False
-
-# d3d8.useShadowBuffers = False
-
-

src/util/config/config.cpp

@@ -1014,11 +1014,6 @@ namespace dxvk {
     { R"(\\indy\.exe$)", {{
       { "d3d9.enableDialogMode",            "True" },
     }} },
-    /* Tom Clancy's Splinter Cell                *
-     * Supports shadow buffers                   */
-    { R"(\\splintercell\.exe$)", {{
-      { "d3d8.useShadowBuffers",            "True" },
-    }} },
     /* Anito: Defend a Land Enraged              */
     { R"(\\Anito\.exe$)", {{
       { "d3d9.memoryTrackTest",             "True" },