[lldb] Fix warnings
This patch fixes:
lldb/tools/lldb-rpc-gen/RPCCommon.cpp:197:13: error: unused variable
'CheckTypeForLLDBPrivate' [-Werror,-Wunused-variable]
lldb/tools/lldb-rpc-gen/lldb-rpc-gen.cpp:105:18: error: unused
variable 'HasCallbackParameter' [-Werror,-Wunused-variable]
