Rename Common::FifoQueue to Common::SPSCQueue

Since all queues are FIFO data structures, the name wasn't informative
as to why you'd use it over a normal queue. I originally thought it had
something to do with the hardware graphics FIFO.

This renames it using the common acronym SPSC, which stands for
single-producer single-consumer, and is most commonly used to talk about
lock-free data structures, both of which this is.

Source/Core/DolphinWX/NetPlay/NetWindow.cpp

@@ -33,9 +33,9 @@
 #include "Common/CommonPaths.h"
 #include "Common/CommonTypes.h"
 #include "Common/Config/Config.h"
-#include "Common/FifoQueue.h"
 #include "Common/FileUtil.h"
 #include "Common/MsgHandler.h"
+#include "Common/SPSCQueue.h"
 #include "Common/StringUtil.h"
 
 #include "Core/Config/SYSCONFSettings.h"