[Triton-MLIR][OPTIMIZER] Cleaned up swizzling (#869)

Swizzling is no longer implemented as a separate pass. It is instead
done in a specialized constructor of SharedEncodingAttr, and tested via
google tests instead of triton-opt + filecheck.

In the future we may want to implement it as a pass again once we have
an additional dialect between TritonGPU and LLVM.

lib/Dialect/TritonGPU/Transforms/CMakeLists.txt

@@ -8,7 +8,6 @@ add_mlir_dialect_library(TritonGPUTransforms
   Combine.cpp
   Pipeline.cpp
   Prefetch.cpp
-  Swizzle.cpp
   TritonGPUConversion.cpp
 
   DEPENDS