Remove redundant parentheses in pending cops message

Follow up to #8414.

Perhaps the parentheses used in the old plain-text format message remain.
In the current YAML format comment it would look redundant.

## Past

```console
- Gemspec/DateAssignment (1.10)
```

## Present

```console
Gemspec/DateAssignment: # (new in 1.10)
  Enabled: true
```

## Future

```console
Gemspec/DateAssignment: # new in 1.10
  Enabled: true
```

lib/rubocop/config_loader.rb

@@ -161,7 +161,7 @@ def warn_on_pending_cops(pending_cops)
       def warn_pending_cop(cop)
         version = cop.metadata['VersionAdded'] || 'N/A'
 
-        warn Rainbow("#{cop.name}: # (new in #{version})").yellow
+        warn Rainbow("#{cop.name}: # new in #{version}").yellow
         warn Rainbow('  Enabled: true').yellow
       end
 

spec/rubocop/cli/options_spec.rb

@@ -415,7 +415,7 @@ class SomeCop < Cop
               remaining_range = pending_cop_warning.length..-(inspected_output.length + 1)
               pending_cops = output[remaining_range]
 
-              expect(pending_cops).to include("Style/SomeCop: # (new in 0.80)\n  Enabled: true")
+              expect(pending_cops).to include("Style/SomeCop: # new in 0.80\n  Enabled: true")
 
               manual_url = output[remaining_range].split("\n").last
 
@@ -433,7 +433,7 @@ class SomeCop < Cop
               remaining_range = pending_cop_warning.length..-(inspected_output.length + 1)
               pending_cops = output[remaining_range]
 
-              expect(pending_cops).to include("Style/SomeCop: # (new in N/A)\n  Enabled: true")
+              expect(pending_cops).to include("Style/SomeCop: # new in N/A\n  Enabled: true")
 
               manual_url = output[remaining_range].split("\n").last