[lldb/Plugins] Clean-up Scripted Process interface requirements (NFC)

The goal of the simple patch is to clean-up the scripted process
interface by removing methods that were introduced with the interface
originally, but that were never really implemented (get_thread_with_id &
get_registers_for_thread).

This patch also changes `get_memory_region_containing_address` to have a
base implementation (that retunrs `None`), instead of forcing the user
to override it in their derived class.

Signed-off-by: Med Ismail Bennani <medismail.bennani@gmail.com>

lldb/source/Plugins/ScriptInterpreter/Python/ScriptedProcessPythonInterface.h

@@ -47,12 +47,9 @@ public:
 
   StructuredData::DictionarySP GetThreadsInfo() override;
 
-  StructuredData::DictionarySP GetThreadWithID(lldb::tid_t tid) override;
-
-  StructuredData::DictionarySP GetRegistersForThread(lldb::tid_t tid) override;
-
   lldb::DataExtractorSP ReadMemoryAtAddress(lldb::addr_t address, size_t size,
                                             Status &error) override;
+                                         
 
   StructuredData::ArraySP GetLoadedImages() override;