Allow installd to delete from preloads/file_cache

When clearing cache, installd should be able to search for and delete
files in /data/preloads/file_cache

Test: Manually trigger installd freeCache
Bug: 31008665
Change-Id: I4c345cc8b0f7a6a8702a55f4720d21283c9d502a

public/installd.te

@@ -130,6 +130,11 @@ allow installd permission_service:service_manager find;
 allow installd block_device:dir { search };
 allow installd labeledfs:filesystem { quotaget quotamod };
 
+# Allow installd to delete from /data/preloads when trimming data caches
+# TODO b/34690396 Remove when time-based purge policy for preloads is implemented in system_server
+allow installd preloads_data_file:file { r_file_perms unlink };
+allow installd preloads_data_file:dir { r_dir_perms write remove_name rmdir };
+
 ###
 ### Neverallow rules
 ###