Compacting non-existant variables in WP_Upgrader::install_package()

[jdgrimes]

WP_Upgrader::install_package() calls compact() with a list of variables, some of which have never existed since this code was added in [11005]. This doesn't cause any problems, as non-existent variables are silently ignored by compact(), but it is quite confusing (I don't know what performance implications might be, but that is trivial anyway).

The following variables don't exist:

• 'local_source'
• 'source_name'
• 'delete_source_dir'

[dd32]

In 31327:

WP_Upgrader: Remove references to non-existant variables that have never existed.
Props jdgrimes. Fixes #29087