ZVISION: Remove dead code, and fix bad usage of assert()

Since some compilers, like MSVC, strip out asserts in non-debug builds,
it's a bad idea to perform active commands within assert() statements.
In this particular case, the engine would attempt to open a file in an
assert statement

engines/zvision/sound/zork_raw.cpp

@@ -213,7 +213,6 @@ RawZorkStream::RawZorkStream(uint32 rate, bool stereo, DisposeAfterUse::Flag dis
 }
 
 int RawZorkStream::readBuffer(int16 *buffer, const int numSamples) {
-
 	int32 bytesRead = _streamReader.readBuffer(buffer, _stream.get(), numSamples);
 
 	if (_stream->eos())
@@ -241,16 +240,10 @@ Audio::RewindableAudioStream *makeRawZorkStream(Common::SeekableReadStream *stre
 	return new RawZorkStream(rate, stereo, disposeAfterUse, stream);
 }
 
-Audio::RewindableAudioStream *makeRawZorkStream(const byte *buffer, uint32 size,
-        int rate,
-        bool stereo,
-        DisposeAfterUse::Flag disposeAfterUse) {
-	return makeRawZorkStream(new Common::MemoryReadStream(buffer, size, disposeAfterUse), rate, stereo, DisposeAfterUse::YES);
-}
-
 Audio::RewindableAudioStream *makeRawZorkStream(const Common::String &filePath, ZVision *engine) {
 	Common::File *file = new Common::File();
-	assert(engine->getSearchManager()->openFile(*file, filePath));
+	if (!engine->getSearchManager()->openFile(*file, filePath))
+		error("File not found: %s", filePath.c_str());
 
 	// Get the file name
 	Common::StringTokenizer tokenizer(filePath, "/\\");

engines/zvision/sound/zork_raw.h

@@ -122,20 +122,6 @@ class RawZorkStream : public Audio::RewindableAudioStream {
 	bool rewind();
 };
 
-/**
- * Creates an audio stream, which plays from the given buffer.
- *
- * @param buffer     Buffer to play from.
- * @param size       Size of the buffer in bytes.
- * @param rate       Rate of the sound data.
- * @param dispose    AfterUse Whether to free the buffer after use (with free!).
- * @return           The new SeekableAudioStream (or 0 on failure).
- */
-Audio::RewindableAudioStream *makeRawZorkStream(const byte *buffer, uint32 size,
-        int rate,
-        bool stereo,
-        DisposeAfterUse::Flag disposeAfterUse = DisposeAfterUse::YES);
-
 /**
  * Creates an audio stream, which plays from the given stream.
  *