Remove unused import

Should have been part of 271acb5

Author: 0xced

tests/Log4NetTextFormatterTest.cs

@@ -6,7 +6,6 @@
 using System.Threading.Tasks;
 using FluentAssertions;
 using Serilog.Core;
-using Serilog.Enrichers;
 using Serilog.Events;
 using Serilog.Parsing;
 using VerifyTests;