fix: remove broken tabbed dashboard

[betodealmeida]

SUMMARY

The tabbed dashboard has been broken for months. This PR removes it. There are other examples of tabbed dashboards, so it should be fine.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

N/A

TEST PLAN

$ superset load-examples

Dashboard is no longer there.

ADDITIONAL INFORMATION

• Has associated issue:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[codecov]

Codecov Report

Merging #14676 (2a5a0e1) into master (eb9dafc) will increase coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #14676      +/-   ##
==========================================
+ Coverage   77.55%   77.58%   +0.03%     
==========================================
  Files         958      957       -1     
  Lines       48549    48528      -21     
  Branches     5702     5703       +1     
==========================================
+ Hits        37651    37652       +1     
+ Misses      10697    10676      -21     
+ Partials      201      200       -1     

Flag	Coverage Δ
hive	81.18% <ø> (+0.06%)	⬆️
javascript	72.52% <ø> (+0.01%)	⬆️
mysql	81.45% <ø> (+0.06%)	⬆️
postgres	81.47% <ø> (+0.06%)	⬆️
presto	81.16% <ø> (+0.06%)	⬆️
python	82.00% <ø> (+0.06%)	⬆️
sqlite	81.09% <ø> (+0.06%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
superset/cli.py	51.72% <ø> (+0.25%)	⬆️
superset/examples/__init__.py	100.00% <ø> (ø)
...rontend/src/components/ListView/Filters/Search.tsx	82.35% <0.00%> (-4.32%)	⬇️
superset/db_engine_specs/presto.py	89.89% <0.00%> (-0.43%)	⬇️
...plore/components/controls/OptionControls/index.tsx	90.42% <0.00%> (-0.11%)	⬇️
...nd/src/explore/components/ExploreViewContainer.jsx	2.32% <0.00%> (-0.02%)	⬇️
superset/databases/schemas.py	99.54% <0.00%> (ø)
superset-frontend/src/common/components/index.tsx	100.00% <0.00%> (ø)
...uperset-frontend/src/components/Menu/MenuRight.tsx	93.18% <0.00%> (ø)
...set-frontend/src/explore/components/ControlRow.tsx	100.00% <0.00%> (ø)
... and 10 more

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