Missing string when uploading files

[SharkyKZ]

Summary of Changes

Remove com_media string as we have an identical global string.
Use global string in filesystem plugin.

Testing Instructions

Try to upload a file with allowed extension but disallowed MIME type.

Actual result BEFORE applying this Pull Request

Untranslated error message:

COM_MEDIA_ERROR_UNABLE_TO_UPLOAD_FILE

Expected result AFTER applying this Pull Request

Translated error message:

Unable to upload file.

Documentation Changes Required

No.

[infograf768]

I have tested this item ✅ successfully on 4f1b87e

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[ghost]

I have tested this item ✅ successfully on 4f1b87e

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/30671.}

[infograf768]

rtc

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/30671.}