Fix logspam when user removed before CE storage prepared

Due to frameworks/base commit 5c65b1ee1023 ("Don't prepare CE storage on
user creation") (http://ag/20241697), removing a user immediately after
creating it causes the user's directories to be destroyed before CE
storage was prepared.

Functionally this works fine; however, it causes some error messages to
be spammed to the log because 'vold_prepare_subdirs destroy' doesn't
like that /data/misc_ce/$userId and /data/vendor_ce/$userId don't exist.
vold_prepare_subdirs logs two error messages itself, but it also exits
with a failure status, which bubbles up and causes a Slog.wtf with a
stack trace in StorageManagerService.

Fix this by making rmrf_contents() simply return true if the directory
doesn't exist.

Bug: 232452368
Test: 'pm create-user 10 && pm remove-user 10' and check logcat
Change-Id: I867a915f4b25e1a5f0603fbd84680b673ff5eb96

vold_prepare_subdirs.cpp

@@ -114,6 +114,9 @@ static bool prepare_dir(struct selabel_handle* sehandle, mode_t mode, uid_t uid,
 static bool rmrf_contents(const std::string& path) {
     auto dirp = std::unique_ptr<DIR, int (*)(DIR*)>(opendir(path.c_str()), closedir);
     if (!dirp) {
+        if (errno == ENOENT) {
+            return true;
+        }
         PLOG(ERROR) << "Unable to open directory: " << path;
         return false;
     }