[hlsl] Remove UserCall handling in DecomposeMemoryAccess.

With the addition of the DirectVariableAccess transform we should not
get a `UserCall` using a storage variable anymore, they should have all
been removed.  This Cl removes the `UserCall` option inside
DecomposeMemoryAccess so we'll get an ICE if we end up here incorrectly.

Bug: 349867642
Change-Id: I0b3f79171788ae3390ec68003a52beb885363af5
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/196635
Commit-Queue: dan sinclair <dsinclair@chromium.org>
Reviewed-by: James Price <jrprice@google.com>
diff --git a/src/tint/lang/hlsl/writer/raise/decompose_memory_access.cc b/src/tint/lang/hlsl/writer/raise/decompose_memory_access.cc
index 089baa8..c71c963 100644
--- a/src/tint/lang/hlsl/writer/raise/decompose_memory_access.cc
+++ b/src/tint/lang/hlsl/writer/raise/decompose_memory_access.cc
@@ -383,25 +383,12 @@
                     insert_load(ld, byte_offset);
                 },
 
-                [&](core::ir::UserCall*) {
-                    if (a->Result(0)->Type()->Is<core::type::Pointer>()) {
-                        // TODO(dsinclair): Passing a pointer into a function, re-write.
-
-                        // Create a new call
-                        // Copy the args, skip the index which is the usage.index
-
-                    } else {
-                        TINT_UNREACHABLE();
-                    }
-                },  //
-
                 [&](core::ir::StoreVectorElement*) {
                     // TODO(dsinclair): Handle stor vector elements
                 },  //
                 [&](core::ir::Store*) {
                     // TODO(dsinclair): Handle store
                 },  //
-
                 TINT_ICE_ON_NO_MATCH);
         }