Remove some unneeded includes

Alc/ALu.c

@@ -46,8 +46,6 @@
 #include "cpu_caps.h"
 #include "bsinc_inc.h"
 
-#include "backends/base.h"
-
 
 /* Cone scalar */
 ALfloat ConeScale = 1.0f;

Alc/backends/base.h

@@ -3,8 +3,6 @@
 
 #include "alMain.h"
 
-#ifdef __cplusplus
-
 #include <string>
 #include <mutex>
 
@@ -116,6 +114,4 @@ struct BackendFactory {
     virtual ALCbackend *createBackend(ALCdevice *device, ALCbackend_Type type) = 0;
 };
 
-
-#endif /* __cplusplus */
 #endif /* AL_BACKENDS_BASE_H */

Alc/inldefs.c

@@ -8,8 +8,6 @@
 #include "alBuffer.h"
 #include "alEffect.h"
 
-#include "backends/base.h"
-
 /* This is a place to dump inline function instantiations, to generate function
  * bodies for calls that can't be inlined. C++ does not have a way to do this
  * explicitly, so as long as there is C code calling inline functions, a body