WavAudioImporter: MSVC WHAT THE HELL.

On this day, MSVC linker started complaining about missing symbols like
WavImporter::doOpenData() in the WavHeaderTest. Mind you, there's
NOTHING the WavHeader.h would use from there. Neither the test. The only
thing that connects those two together is that WavHeader.h includes
WavImporter.h (probably just a leftover from the time where those two
actually depended on each other). My suspicion is that this got
triggered due to recent changes in AbstractPlugin (it's movable now) and
MSVC attempts to instantiate the destructor or whatnot, needing
references to the privately defined virtual functions. Or something. All
that while nothing from there is EVER used.

Removing the header dependency, hopefully this fixes it. Ugh.

src/MagnumPlugins/WavAudioImporter/WavHeader.cpp

@@ -27,8 +27,6 @@
 
 #include <Corrade/Utility/Debug.h>
 
-#include "Magnum/Magnum.h"
-
 namespace Magnum { namespace Audio { namespace Implementation {
 
 static_assert(sizeof(RiffChunk) == 8, "RiffChunk size is not 8 bytes");

src/MagnumPlugins/WavAudioImporter/WavHeader.h

@@ -26,7 +26,7 @@
     DEALINGS IN THE SOFTWARE.
 */
 
-#include "MagnumPlugins/WavAudioImporter/WavImporter.h"
+#include "Magnum/Magnum.h"
 
 namespace Magnum { namespace Audio { namespace Implementation {