[Global Opt] Turn on transpose propagation by default (iree-org#19253)

From the discussion on iree-org#19250, this
should be made default. Testing locally revealed no regressions and the
benchmarks from the linked issue have been removed
(iree-org#15973).

Signed-off-by: Ian Wood <ianwood2024@u.northwestern.edu>

compiler/src/iree/compiler/GlobalOptimization/Passes.cpp

@@ -29,12 +29,11 @@ static llvm::cl::opt<bool> clEnableFuseSiluHorizontalMatmul(
     llvm::cl::desc(
         "Enables fusing specifically structured matmuls (experimental)."),
     llvm::cl::init(false));
-// TODO(#15973): Make default to true after fixing the CPU DT regression.
 static llvm::cl::opt<bool> clEnableTransposePropagation(
     "iree-global-opt-propagate-transposes",
     llvm::cl::desc(
         "Enables propagation of transpose ops to improve fusion chances."),
-    llvm::cl::init(false));
+    llvm::cl::init(true));
 
 // TODO(hanchung): Remove the flag. We don't want to do early materialization by
 // default. Because it won't work for heterogeneous computing. This is not the