Recent commit acd9525e9 has removed all references to max_fds
therefore remove it, moreover clang18 is happier
| ../../elfutils-0.191/debuginfod/debuginfod.cxx:1448:8: error: private field 'max_fds' is not used [-Werror,-Wunused-private-field]
| 1448 | long max_fds;
| | ^
| 1 error generated.