[mhlo] Drop unnecessary build dependencies (#12728)

Also update the bazel-cmake target mapping to avoid pulling in unused
cmake targets.

Issue: https://github.com/openxla/iree/issues/12678
diff --git a/build_tools/bazel_to_cmake/bazel_to_cmake_targets.py b/build_tools/bazel_to_cmake/bazel_to_cmake_targets.py
index fd5884e..9948c76 100644
--- a/build_tools/bazel_to_cmake/bazel_to_cmake_targets.py
+++ b/build_tools/bazel_to_cmake/bazel_to_cmake_targets.py
@@ -84,11 +84,6 @@
         "ChloOps",
         "MhloDialect",
     ],
-    "@mlir-hlo//:map_lmhlo_to_scalar_op": [
-        "tensorflow::external_mhlo_includes",
-        "LmhloDialect",  # Unfortunate.
-        "MhloDialect",
-    ],
     "@mlir-hlo//:map_mhlo_to_scalar_op": [
         "tensorflow::external_mhlo_includes",
         "MhloDialect",
@@ -97,12 +92,12 @@
         "tensorflow::external_mhlo_includes",
         "MhloPasses",
         "MhloShapeOpsToStandard",
-        "MhloToArithmeticConversion",
-        "MhloToLhloConversion",
         "MhloToLinalg",
-        "MhloToMemrefConversion",
         "MhloToStandard",
         "StablehloToMhlo",
+        # Note: We deliberately omit some passes that we do not use in IREE,
+        # e.g.: MhloToArithmeticConversion, MhloToLhloConversion, or
+        # MhloToMemrefConversion.
     ],
     "@mlir-hlo//:unfuse_batch_norm": [
         "tensorflow::external_mhlo_includes",
diff --git a/compiler/src/iree/compiler/InputConversion/MHLO/BUILD.bazel b/compiler/src/iree/compiler/InputConversion/MHLO/BUILD.bazel
index 7912457..1cbd07c 100644
--- a/compiler/src/iree/compiler/InputConversion/MHLO/BUILD.bazel
+++ b/compiler/src/iree/compiler/InputConversion/MHLO/BUILD.bazel
@@ -100,11 +100,9 @@
         "@llvm-project//mlir:Transforms",
         "@mlir-hlo//:chlo_legalize_to_hlo",
         "@mlir-hlo//:map_chlo_to_hlo_op",
-        "@mlir-hlo//:map_lmhlo_to_scalar_op",
         "@mlir-hlo//:map_mhlo_to_scalar_op",
         "@mlir-hlo//:mhlo_passes",
         "@mlir-hlo//:mlir_hlo",
-        "@mlir-hlo//:unfuse_batch_norm",
         "@mlir-hlo//stablehlo:broadcast_utils",
         "@mlir-hlo//stablehlo:chlo_ops",
     ],
diff --git a/compiler/src/iree/compiler/InputConversion/MHLO/CMakeLists.txt b/compiler/src/iree/compiler/InputConversion/MHLO/CMakeLists.txt
index 4afeac3..b3dc7f1 100644
--- a/compiler/src/iree/compiler/InputConversion/MHLO/CMakeLists.txt
+++ b/compiler/src/iree/compiler/InputConversion/MHLO/CMakeLists.txt
@@ -59,7 +59,6 @@
     IREELinalgExtDialect
     IREELinalgExtPasses
     LLVMSupport
-    LmhloDialect
     MLIRAffineDialect
     MLIRAffineUtils
     MLIRArithDialect
@@ -87,10 +86,7 @@
     MhloDialect
     MhloPasses
     MhloShapeOpsToStandard
-    MhloToArithmeticConversion
-    MhloToLhloConversion
     MhloToLinalg
-    MhloToMemrefConversion
     MhloToStandard
     StablehloBroadcastUtils
     StablehloToMhlo
diff --git a/compiler/src/iree/compiler/Tools/BUILD.bazel b/compiler/src/iree/compiler/Tools/BUILD.bazel
index bfd07e9..a3294fd 100644
--- a/compiler/src/iree/compiler/Tools/BUILD.bazel
+++ b/compiler/src/iree/compiler/Tools/BUILD.bazel
@@ -43,7 +43,6 @@
         "@llvm-project//mlir:ConversionPasses",
         "@llvm-project//mlir:IR",
         "@llvm-project//mlir:TosaDialect",
-        "@mlir-hlo//:lhlo",
         "@mlir-hlo//:mlir_hlo",
         "@mlir-hlo//stablehlo:chlo_ops",
         "@mlir-hlo//stablehlo:stablehlo_ops",