DiscIO: Make factory methods return unique_ptrs

Rather than rely on the developer to do the right thing,
just make the default behavior safely deallocate resources.

If shared semantics are ever needed in the future, the
constructor that takes a unique_ptr for shared_ptr can
be used.

Source/Core/DiscIO/FileBlob.cpp

@@ -2,6 +2,7 @@
 // Licensed under GPLv2+
 // Refer to the license.txt file included.
 
+#include <memory>
 #include <string>
 #include "DiscIO/FileBlob.h"
 
@@ -14,13 +15,13 @@ PlainFileReader::PlainFileReader(std::FILE* file)
 	m_size = m_file.GetSize();
 }
 
-PlainFileReader* PlainFileReader::Create(const std::string& filename)
+std::unique_ptr<PlainFileReader> PlainFileReader::Create(const std::string& filename)
 {
 	File::IOFile f(filename, "rb");
 	if (f)
-		return new PlainFileReader(f.ReleaseHandle());
-	else
-		return nullptr;
+		return std::unique_ptr<PlainFileReader>(new PlainFileReader(f.ReleaseHandle()));
+
+	return nullptr;
 }
 
 bool PlainFileReader::Read(u64 offset, u64 nbytes, u8* out_ptr)