Do not force trailing comma when using mixed layout

Cargo.lock

@@ -1,3 +1,5 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
 [[package]]
 name = "aho-corasick"
 version = "0.6.9"

src/overflow.rs

@@ -607,9 +607,6 @@ impl<'a> Context<'a> {
             tactic
         } else if !self.context.use_block_indent() {
             SeparatorTactic::Never
-        } else if tactic == DefinitiveListTactic::Mixed {
-            // We are using mixed layout because everything did not fit within a single line.
-            SeparatorTactic::Always
         } else {
             self.context.config.trailing_comma()
         };

tests/source/trailing-comma-never.rs

@@ -39,3 +39,7 @@ enum StructY {
         i: i32,
     }
 }
+
+static XXX: [i8; 64] = [
+1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,1, 1, 1,
+];

tests/target/trailing-comma-never.rs

@@ -29,3 +29,7 @@ enum StructY {
     A { s: u16 },
     B { u: u32, i: i32 }
 }
+
+static XXX: [i8; 64] = [
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1
+];