various: do not include file names directly in error messages

git grep -l 'Failed to open /'|xargs sed -r -i 's|"Failed to open (/[^ ]+): %m"|"Failed to open %s: %m", "\1"|g'
git grep -l $'Failed to open \'/'|xargs sed -r -i $'s|"Failed to open \'(/[^ ]+)\': %m"|"Failed to open %s: %m", "\\1"|g'
git grep -l "Failed to open /"|xargs sed -r -i $'s|"Failed to open (/[^ ]+), ignoring: %m"|"Failed to open %s, ignoring: %m", "\\1"|g'
+ some manual fixups.

src/tmpfiles/tmpfiles.c

@@ -466,7 +466,7 @@ static int load_unix_sockets(Context *c) {
         f = fopen("/proc/net/unix", "re");
         if (!f)
                 return log_full_errno(errno == ENOENT ? LOG_DEBUG : LOG_WARNING, errno,
-                                      "Failed to open /proc/net/unix, ignoring: %m");
+                                      "Failed to open %s, ignoring: %m", "/proc/net/unix");
 
         /* Skip header */
         r = read_line(f, LONG_LINE_MAX, NULL);