Tweak autocorrection for Style/RedundantBegin

This PR tweaks autocorrection for `Style/RedundantBegin`
when using endless method definition with redundant `begin`.

```ruby
def foo = begin
  bar
end
```

## Before

```console
% bundle exec rubocop --only Style/RedundantBegin -a
(snip)

example.rb:1:11: C: [Corrected] Style/RedundantBegin: Redundant begin block detected.
def foo = begin
          ^^^^^

1 file inspected, 1 offense detected, 1 offense corrected
```

```ruby
def foo =
  bar
```

## After

```ruby
def foo =  bar
```

This would be more closer to a one-liner endless idiom.

lib/rubocop/cop/style/redundant_begin.rb

@@ -114,7 +114,7 @@ def register_offense(node)
             if node.parent&.assignment?
               replace_begin_with_statement(corrector, offense_range, node)
             else
-              corrector.remove(offense_range)
+              remove_begin(corrector, offense_range, node)
             end
 
             if use_modifier_form_after_multiline_begin_block?(node)
@@ -136,6 +136,14 @@ def replace_begin_with_statement(corrector, offense_range, node)
           restore_removed_comments(corrector, offense_range, node, first_child)
         end
 
+        def remove_begin(corrector, offense_range, node)
+          if node.parent.respond_to?(:endless?) && node.parent.endless?
+            offense_range = range_with_surrounding_space(offense_range, newlines: true)
+          end
+
+          corrector.remove(offense_range)
+        end
+
         # Restore comments that occur between "begin" and "first_child".
         # These comments will be moved to above the assignment line.
         def restore_removed_comments(corrector, offense_range, node, first_child)

spec/rubocop/cop/style/redundant_begin_spec.rb

@@ -579,7 +579,7 @@ def foo = begin
         end
       RUBY
 
-      expect_correction("def foo = \n  bar\n\n")
+      expect_correction("def foo =  bar\n\n")
     end
 
     it 'accepts when `begin` block has multiple statements' do