Revert "find_psr4_file: Quick exit if psr4_map is not populated (#39646)"

[mreishus]

This reverts commit c647351.

Fixes #

Proposed changes:

• This reverts commit c647351.

Other information:

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[github-actions]

Are you an Automattician? Please test your changes on all WordPress.com environments to help mitigate accidental explosions.

• To test on WoA, go to the Plugins menu on a WordPress.com Simple site. Click on the "Upload" button and follow the upgrade flow to be able to upload, install, and activate the Jetpack Beta plugin. Once the plugin is active, go to Jetpack > Jetpack Beta, select your plugin, and enable the revert/c647351719be15f176431cf989428f2d19841206 branch.

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[github-actions]

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