Remove usages of deprecatedWriter

lib/std/crypto/benchmark.zig

@@ -460,7 +460,8 @@ fn mode(comptime x: comptime_int) comptime_int {
 }
 
 pub fn main() !void {
-    var stdout_buffer: [4096]u8 = undefined;
+    // Size of buffer is about size of printed message.
+    var stdout_buffer: [0x100]u8 = undefined;
     var stdout_writer = std.fs.File.stdout().writer(&stdout_buffer);
     const stdout = &stdout_writer.interface;