Address Layout/TrailingWhitespace offense

This commit addresses the following RuboCop offense reported at:
https://buildkite.com/rails/rails/builds/110044#019140ca-55c0-4172-9b4f-f8422dd34559/1215-1221

```ruby
$ bundle exec rubocop -a activesupport/lib/active_support/json/encoding.rb
Inspecting 1 file
C

Offenses:

activesupport/lib/active_support/json/encoding.rb:34:1: C: [Corrected] Layout/EmptyLinesAroundMethodBody: Extra empty line detected at method body end.
activesupport/lib/active_support/json/encoding.rb:34:1: C: [Corrected] Layout/TrailingWhitespace: Trailing whitespace detected.

1 file inspected, 2 offenses detected, 2 offenses corrected
$
```

Follow up rails#51272

activesupport/lib/active_support/json/encoding.rb

@@ -31,7 +31,6 @@ class JSONGemEncoder # :nodoc:
 
         def initialize(options = nil)
           @options = options || {}
-
         end
 
         # Encode the given object into a JSON string