Hide a few symbols, no need for extern "C" there

Signed-off-by: falkTX <falktx@gmail.com>

source/backend/plugin/CarlaPluginNative.cpp

@@ -27,10 +27,10 @@ using water::jmax;
 using water::String;
 using water::StringArray;
 
-CARLA_EXTERN_C
-std::size_t carla_getNativePluginCount() noexcept;
+// -----------------------------------------------------------------------
+// used in carla-base.cpp
 
-CARLA_EXTERN_C
+std::size_t carla_getNativePluginCount() noexcept;
 const NativePluginDescriptor* carla_getNativePluginDescriptor(const std::size_t index) noexcept;
 
 // -----------------------------------------------------------------------

source/plugin/carla-base.cpp

@@ -25,10 +25,8 @@
 #ifdef CARLA_NATIVE_PLUGIN_LV2
 #include "lv2/lv2.h"
 
-CARLA_EXTERN_C
+// defined in CarlaPluginNative.cpp
 std::size_t carla_getNativePluginCount() noexcept;
-
-CARLA_EXTERN_C
 const NativePluginDescriptor* carla_getNativePluginDescriptor(const std::size_t index) noexcept;
 #endif