[lldb][ObjC][NFC] Fix c++20 gcc compile errors

When compiling with gcc 11+ and -DCMAKE_CXX_STANDARD=20, errors
like the following happened:
```
llvm-project/lldb/source/Plugins/Language/ObjC/NSDictionary.cpp:1063:5: error: template-id not allowed for destructor
 1063 |     ~GenericNSDictionaryMSyntheticFrontEnd<D32,D64>() {
      |     ^
```
This appears to be something only gcc enforces and only from 11 and beyond.

This changes fixes all the instances of this pattern by removing the
template arguments.