[4.0] Remove deprecated client handling from the updater extension adapter class

[zero-24]

Summary of Changes

Remove deprecated client handling from the updater extension adapter class

Testing Instructions

• install an outdated version of any extension
• make sure you can update it.
• apply this patch
• install another outdated version on an extension
• make sure you can stull update
• install an outdated extension that still uses the numeric client stuff
• confirm that now breaks as expected.

Expected result

the client value only accepts site and administrator and no numeric id any more

Actual result

there is still lagacy behavior in the extensionadapter class.

Documentation Changes Required

This has to be documented as B/C break.

cc @wilsonge IIRC this has to go in before beta when accepted right?

[wilsonge]

Yes it does. Thanks!

[zero-24]

This has been documented: https://docs.joomla.org/Potential_backward_compatibility_issues_in_Joomla_4#Updater