patch_manager: Make a few functions internally linked

These functions are only used within this translation unit, so we can
make them internally linked.

src/core/file_sys/patch_manager.h

@@ -22,18 +22,6 @@ namespace FileSys {
 class NCA;
 class NACP;
 
-enum class TitleVersionFormat : u8 {
-    ThreeElements, ///< vX.Y.Z
-    FourElements,  ///< vX.Y.Z.W
-};
-
-std::string FormatTitleVersion(u32 version,
-                               TitleVersionFormat format = TitleVersionFormat::ThreeElements);
-
-// Returns a directory with name matching name case-insensitive. Returns nullptr if directory
-// doesn't have a directory with name.
-VirtualDir FindSubdirectoryCaseless(VirtualDir dir, std::string_view name);
-
 // A centralized class to manage patches to games.
 class PatchManager {
 public: