Fix: optimize runtime code when dataLoader is not defined

[ClarkXia]

The dataLoader runtime is unnecessary when dataLoader is not exported.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 90.90909% with 4 lines in your changes are missing coverage. Please review.

❗ No coverage uploaded for pull request base (release/next@ee14962). Click here to learn what that means.

Files	Patch %	Lines
packages/runtime/src/appData.ts	80.00%	2 Missing ⚠️
packages/runtime/src/runClientApp.tsx	50.00%	2 Missing ⚠️

Additional details and impacted files

@@               Coverage Diff               @@
##             release/next    #6849   +/-   ##
===============================================
  Coverage                ?   79.11%           
===============================================
  Files                   ?      221           
  Lines                   ?    19745           
  Branches                ?     2508           
===============================================
  Hits                    ?    15622           
  Misses                  ?     4086           
  Partials                ?       37           

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