restapps install fails if bad symlink exists

Attempting to install resapps fails with:

Downloading module 'restapps'
Processing restapps
Verifying local module download...Verified
Extracting...Done
Download completed in 1 seconds
checking for timestamp field..already exists
In install.php line 103:
  symlink(): No such file or directory

It was caused by an existing bad symlink, probably as a result of restoring an HA backup to a standalone install:

lrwxrwxrwx 1 asterisk asterisk   53 Sep 15 19:27 image.php -> /drbd/httpd/www/html/admin/modules/restapps/image.php

# ll /drbd/httpd/www/html/admin/modules/restapps/image.php
ls: cannot access /drbd/httpd/www/html/admin/modules/restapps/image.php: No such file or directory

removing the symlink /var/www/html/restapps/image.php allows the install to proceed.