🧹 DiabloUI/progress.cpp: Move to anonymous namespace

Also removes the unused `char dialogText[256];`

Source/DiabloUI/progress.cpp

@@ -9,9 +9,8 @@
 #include "utils/display.h"
 
 namespace devilution {
-
+namespace {
 Art dialogArt;
-char dialogText[256];
 Art progressArt;
 Art ArtPopupSm;
 Art ArtProgBG;
@@ -89,6 +88,8 @@ void progress_Render(BYTE progress)
 	}
 }
 
+} // namespace
+
 bool UiProgressDialog(const char *msg, int (*fnfunc)(), int rate)
 {
 	progress_Load(msg);