Deprecate MatrixSliceMutN

There is no other type alias with this naming convention. I believe it
is a remnant from the past, when we had e.g. MatrixN type aliases. But
these no longer exist, therefore I believe this alias should also be
removed, instead of updated to "MatrixViewMutN".

src/base/alias_slice.rs

@@ -378,6 +378,7 @@ pub type MatrixSliceMutMN<'a, T, R, C, RStride = U1, CStride = R> =
 /// A column-major matrix slice with `D` rows and columns.
 ///
 /// **Because this is an alias, not all its methods are listed here. See the [`Matrix`](crate::base::Matrix) type too.**
+#[deprecated = "Use MatrixViewMut instead."]
 pub type MatrixSliceMutN<'a, T, D, RStride = U1, CStride = D> =
     Matrix<T, D, D, ViewStorageMut<'a, T, D, D, RStride, CStride>>;