Studio: Remove noop menu items from topbar

[katinthehatsite]

Related issues

Fixes STU-1954

How AI was used in this PR

It was used to update tests. Otherwise, not need as the change is simple.

Proposed Changes

This PR remove noop menu items such as "Show Tab Bar", "Show All Tabs", "Show Previous Tab", "Show Next Tab", "Move Tab to New Window", "Merge All Windows" as they are not needed with Studio being a single window application.

Testing Instructions

• Pull the changes from this branch
• Start Studio with npm start
• Confirm that the topbar does not contain the elements mentioned above:

Pre-merge Checklist

• Have you checked for TypeScript, React or other console errors?

[wojtekn]

The code change looks clear.

[wpmobilebot]

📊 Performance Test Results

Comparing 4b7f5c4 vs trunk

app-size

Metric	trunk	4b7f5c4	Diff	Change
App Size (Mac)	1316.83 MB	1316.83 MB	0.00 MB	⚪ 0.0%

site-editor

Metric	trunk	4b7f5c4	Diff	Change
load	744 ms	760 ms	+16 ms	⚪ 0.0%

site-startup

Metric	trunk	4b7f5c4	Diff	Change
siteCreation	6510 ms	6484 ms	26 ms	⚪ 0.0%
siteStartup	1862 ms	1862 ms	0 ms	⚪ 0.0%

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Results are median values from multiple test runs.

Legend: 🟢 Improvement (faster) | 🔴 Regression (slower) | ⚪ No change (<50ms diff)