tidy: Modernize code to eliminate "use using" warning.

Convert an old style "typedef" statement into a modern "using"
statement.  Change made by clang-tidy.

https://clang.llvm.org/extra/clang-tidy/checks/modernize/use-using.html

Author: linuxdude42

mythtv/libs/libmythui/mediamonitor.h

@@ -12,7 +12,7 @@
 #include "libmythbase/mythmedia.h"
 #include "libmythui/mythuiexp.h"
 
-typedef void (*MediaCallback)(MythMediaDevice *mediadevice, bool forcePlayback);
+using MediaCallback = void (*)(MythMediaDevice *, bool);
 
 /// Stores details of media handlers