[cmake][interpreter] Remove CLANG_ENABLE_ARCMT

LLVM removed `ARCMigrate`, do the same in ROOT.

This will get rid of the CMAKE warning when configuring ROOT.

```
CMake Deprecation Warning at interpreter/llvm-project/clang/CMakeLists.txt:456 (message):
  'CLANG_ENABLE_ARCMT' is deprecated as ARCMigrate has been removed from
  Clang.  Please use 'CLANG_ENABLE_OBJC_REWRITER' instead to enable or
  disable the Objective-C rewriter.
```

Ref: llvm/llvm-project@c4a01974

Author: devajithvs

interpreter/CMakeLists.txt

@@ -43,7 +43,6 @@ else()
   set(LLVM_ENABLE_ZSTD FORCE_ON CACHE STRING "Always enabled because it's already a dependency of ROOT" FORCE)
 endif()
 set(CLANG_ENABLE_STATIC_ANALYZER OFF CACHE BOOL "")
-set(CLANG_ENABLE_ARCMT OFF CACHE BOOL "")
 set(LLVM_INCLUDE_TESTS OFF CACHE BOOL "")
 set(LLVM_INCLUDE_BENCHMARKS OFF CACHE BOOL "")
 set(CLANG_INCLUDE_TESTS OFF CACHE BOOL "")