Turn On ImplicitUsings (#2079)

* Turn on ImplicitUsings

* Fix formatting

* Run linter

src/Core/Exceptions/BadRequestException.cs

@@ -1,5 +1,4 @@
-using System;
-using Microsoft.AspNetCore.Mvc.ModelBinding;
+using Microsoft.AspNetCore.Mvc.ModelBinding;
 
 namespace Bit.Core.Exceptions
 {

src/Core/Exceptions/GatewayException.cs

@@ -1,6 +1,4 @@
-using System;
-
-namespace Bit.Core.Exceptions
+namespace Bit.Core.Exceptions
 {
     public class GatewayException : Exception
     {

src/Core/Exceptions/InvalidEmailException.cs

@@ -1,6 +1,4 @@
-using System;
-
-namespace Bit.Core.Exceptions
+namespace Bit.Core.Exceptions
 {
     public class InvalidEmailException : Exception
     {

src/Core/Exceptions/InvalidGatewayCustomerIdException.cs

@@ -1,6 +1,4 @@
-using System;
-
-namespace Bit.Core.Exceptions
+namespace Bit.Core.Exceptions
 {
     public class InvalidGatewayCustomerIdException : Exception
     {

src/Core/Exceptions/NotFoundException.cs

@@ -1,6 +1,4 @@
-using System;
-
-namespace Bit.Core.Exceptions
+namespace Bit.Core.Exceptions
 {
     public class NotFoundException : Exception { }
 }