Remove methods which are not needed anymore

These methods were intended for managing cached entries. Sice it was
decided not to serve caching in the store, these methods are no longer
needed.

libimagstore/src/store.rs

@@ -82,21 +82,6 @@ impl StoreEntry {
     fn is_borrowed(&self) -> bool {
         self.entry == StoreEntryPresence::Borrowed
     }
-
-    /// Flush the entry to disk
-    fn set_entry(&mut self, entry: Entry) -> Result<()> {
-        unimplemented!()
-    }
-
-    /// We borrow the entry
-    fn get_entry(&mut self) -> Result<Entry> {
-        unimplemented!()
-    }
-
-    /// We copy the entry
-    fn copy_entry(&mut self) -> Result<Entry> {
-        unimplemented!()
-    }
 }
 
 /// The Store itself, through this object one can interact with IMAG's entries