build: sort.py: filter empty and duplicate items

Note: This seems to already be done for `protocol` lines.

Before:

    $ ./contrib/sort.py test.profile
    sort.py: checking 1 profile(s)...
    test.profile:1:-private-etc ,,bar,,foo,,bar,,,
    test.profile:1:+private-etc ,,,,,,,bar,bar,foo
    test.profile:2:-protocol ,,unix,,bluetooth,,unix,,inet,,,
    test.profile:2:+protocol unix,inet,bluetooth
    [ Fixed ] test.profile

After:

    $ ./contrib/sort.py test.profile
    sort.py: checking 1 profile(s)...
    test.profile:1:-private-etc ,,bar,,foo,,bar,,,
    test.profile:1:+private-etc bar,foo
    test.profile:2:-protocol ,,unix,,bluetooth,,unix,,inet,,,
    test.profile:2:+protocol unix,inet,bluetooth
    [ Fixed ] test.profile

1 files changed, 1 insertions, 1 deletions

diff --git a/etc/profile-a-l/dnscrypt-proxy.profile b/etc/profile-a-l/dnscrypt-proxy.profile
index 0d52805b7..50b56fb2d 100644
--- a/etc/profile-a-l/dnscrypt-proxy.profile
+++ b/etc/profile-a-l/dnscrypt-proxy.profile
@@ -38,7 +38,7 @@ notv
 nou2f
 novideo
 protocol inet,inet6
-seccomp.drop _sysctl,acct,add_key,adjtimex,clock_adjtime,delete_module,fanotify_init,finit_module,get_mempolicy,init_module,io_cancel,io_destroy,io_getevents,io_setup,io_submit,ioperm,iopl,kcmp,kexec_file_load,kexec_load,keyctl,lookup_dcookie,mbind,migrate_pages,modify_ldt,mount,move_pages,open_by_handle_at,perf_event_open,perf_event_open,pivot_root,process_vm_readv,process_vm_writev,ptrace,remap_file_pages,request_key,set_mempolicy,swapoff,swapon,sysfs,syslog,umount2,uselib,vmsplice
+seccomp.drop _sysctl,acct,add_key,adjtimex,clock_adjtime,delete_module,fanotify_init,finit_module,get_mempolicy,init_module,io_cancel,io_destroy,io_getevents,io_setup,io_submit,ioperm,iopl,kcmp,kexec_file_load,kexec_load,keyctl,lookup_dcookie,mbind,migrate_pages,modify_ldt,mount,move_pages,open_by_handle_at,perf_event_open,pivot_root,process_vm_readv,process_vm_writev,ptrace,remap_file_pages,request_key,set_mempolicy,swapoff,swapon,sysfs,syslog,umount2,uselib,vmsplice
 tracelog
 
 disable-mnt