remove dangling symlink after data upgrade

[lotem]

error report:
rime/squirrel#263 (comment)

the deployment task intent to remove symlinks that pointed to prebuilt binaries in shared directory.
after upgrade to a version with less bundled data, those symlinks became dangling, they should be removed too instead of throwing an error.

[lotem]

手動解決辦法：
rime/squirrel#269 (comment)