[lldb] Drop PY_MINOR_VERSION >= 3 check (NFC)

The minimum supported Python version is now 3.8, so there's no supported
configuration where the minor version is less than 3.

Author: JDevlieghere

lldb/source/Plugins/ScriptInterpreter/Python/PythonDataObjects.cpp

@@ -430,13 +430,8 @@ Expected<llvm::StringRef> PythonString::AsUTF8() const {
 }
 
 size_t PythonString::GetSize() const {
-  if (IsValid()) {
-#if PY_MINOR_VERSION >= 3
+  if (IsValid())
     return PyUnicode_GetLength(m_py_obj);
-#else
-    return PyUnicode_GetSize(m_py_obj);
-#endif
-  }
   return 0;
 }