Revert "Exposing min/max value interface on MultiValuedFastField Reader (#1094)"

This reverts commit bb488305c9.

src/fastfield/multivalued/reader.rs

@@ -46,24 +46,6 @@ impl<Item: FastValue> MultiValuedFastFieldReader<Item> {
         self.vals_reader.get_range_u64(range.start, &mut vals[..]);
     }
 
-    /// Returns the minimum value for this fast field.
-    ///
-    /// The max value does not take in account of possible
-    /// deleted document, and should be considered as an upper bound
-    /// of the actual maximum value.
-    pub fn min_value(&self) -> Item {
-        self.vals_reader.max_value()
-    }
-
-    /// Returns the maximum value for this fast field.
-    ///
-    /// The max value does not take in account of possible
-    /// deleted document, and should be considered as an upper bound
-    /// of the actual maximum value.
-    pub fn max_value(&self) -> Item {
-        self.vals_reader.min_value()
-    }
-
     /// Returns the number of values associated with the document `DocId`.
     pub fn num_vals(&self, doc: DocId) -> usize {
         let range = self.range(doc);