In [38887], installing themes in the Customizer was disabled for multisite installs. However, an update link continues to be displayed when a theme update is available. Clicking the link causes a JavaScript error.
This removes that update link because updates cannot actually be performed in the Customizer in this situation.
Props desrosj, earnjam, mukesh27, audrasjb, garrett-eclipse.
Fixes#46997.
Built from https://develop.svn.wordpress.org/trunk@45527
git-svn-id: http://core.svn.wordpress.org/trunk@45338 1a063a9b-81f0-0310-95a4-ce76da25c4cd