Revert "[mlir] Initial patch to add an MPI dialect (#68892)" (#81884)

This reverts commit 2d616ec.

Buildbot failures:
https://lab.llvm.org/buildbot/#/builders/177/builds/29364

Author: Groverkss

mlir/include/mlir/Dialect/CMakeLists.txt

@@ -21,7 +21,6 @@ add_subdirectory(Math)
 add_subdirectory(MemRef)
 add_subdirectory(Mesh)
 add_subdirectory(MLProgram)
-add_subdirectory(MPI)
 add_subdirectory(NVGPU)
 add_subdirectory(OpenACC)
 add_subdirectory(OpenACCMPCommon)