commonio: free removed database entries

Free the actual struct of the removed entry.

Example userdel report:

    Direct leak of 40 byte(s) in 1 object(s) allocated from:
        #0 0x55b230efe857 in reallocarray (./src/userdel+0xda857)
        #1 0x55b230f6041f in mallocarray ./lib/./alloc.h:97:9
        #2 0x55b230f6041f in commonio_open ./lib/commonio.c:563:7
        #3 0x55b230f39098 in open_files ./src/userdel.c:555:6
        #4 0x55b230f39098 in main ./src/userdel.c:1189:2
        #5 0x7f9b48c64189 in __libc_start_call_main csu/../sysdeps/nptl/libc_start_call_main.h:58:16

lib/commonio.c

@@ -1060,6 +1060,8 @@ int commonio_remove (struct commonio_db *db, const char *name)
 		db->ops->free (p->eptr);
 	}
 
+	free(p);
+
 	return 1;
 }