[lldb] Replace empty ctor en dtor bodies with =default (NFC)

Use = default instead of empty constructor and destructor bodies in the
API layer.
diff --git a/lldb/source/API/SBSourceManager.cpp b/lldb/source/API/SBSourceManager.cpp
index 78e9974..6fe3dac 100644
--- a/lldb/source/API/SBSourceManager.cpp
+++ b/lldb/source/API/SBSourceManager.cpp
@@ -104,7 +104,7 @@
   return LLDB_RECORD_RESULT(*this);
 }
 
-SBSourceManager::~SBSourceManager() {}
+SBSourceManager::~SBSourceManager() = default;
 
 size_t SBSourceManager::DisplaySourceLinesWithLineNumbers(
     const SBFileSpec &file, uint32_t line, uint32_t context_before,