Upgrade/Install: Pass correct argument to `clear_destination` in `Theme_Upgrader::install()`.

Follow-up to [48390].

Props afragen, sabernhardt.
Reviewed by desrosj, SergeyBiryukov.
Merges [48685] to the 5.5 branch.
Fixes #9757.
Built from https://develop.svn.wordpress.org/branches/5.5@48687


git-svn-id: https://core.svn.wordpress.org/branches/5.5@48449 1a063a9b-81f0-0310-95a4-ce76da25c4cd