Remove extern from function declared in headers. (#13790)

By default functions are declared as extern in C/C++ headers. The goal
of this PR is to reduce the wall of text that many headers have and,
more importantly, to make the declaration of extern'd variables - of
which we have many dispersed in various places - easily and quickly
identifiable.

Automatically generated with:

    $ git grep -l '^extern.*(' '**.h' | \
            grep -v libjudy | \
            grep -v 'sqlite3.h' | \
            xargs sed -i -e 's/extern \(.*(.*$\)/\1/'

This is a NFC.

1 files changed, 4 insertions, 4 deletions

diff --git a/collectors/ebpf.plugin/ebpf_cgroup.h b/collectors/ebpf.plugin/ebpf_cgroup.h
index cca9a950d1..5956adee7f 100644
--- a/collectors/ebpf.plugin/ebpf_cgroup.h
+++ b/collectors/ebpf.plugin/ebpf_cgroup.h
@@ -60,10 +60,10 @@ typedef struct ebpf_cgroup_target {
     struct ebpf_cgroup_target *next;
 } ebpf_cgroup_target_t;
 
-extern void ebpf_map_cgroup_shared_memory();
-extern void ebpf_parse_cgroup_shm_data();
-extern void ebpf_close_cgroup_shm();
-extern void ebpf_create_charts_on_systemd(char *id, char *title, char *units, char *family, char *charttype, int order,
+void ebpf_map_cgroup_shared_memory();
+void ebpf_parse_cgroup_shm_data();
+void ebpf_close_cgroup_shm();
+void ebpf_create_charts_on_systemd(char *id, char *title, char *units, char *family, char *charttype, int order,
                                           char *algorithm, char *context, char *module, int update_every);
 
 #endif /* NETDATA_EBPF_CGROUP_H */