Revert "[LLVM][MLIR] Move LSP server support library from MLIR into LLVM (#155572)"

This reverts commit c0aee32.
This reverts commit a0b8d54.

Fails to link with MLIR dylib build.

Author: nikic

llvm/include/llvm/Support/LSP/Transport.h

@@ -135,7 +135,6 @@ if (UNIX AND "${CMAKE_SYSTEM_NAME}" MATCHES "AIX")
 endif()
 
 add_subdirectory(BLAKE3)
-add_subdirectory(LSP)
 
 add_llvm_component_library(LLVMSupport
   ABIBreak.cpp