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, 7 insertions, 7 deletions

diff --git a/libnetdata/circular_buffer/circular_buffer.h b/libnetdata/circular_buffer/circular_buffer.h
index ba3ddd9cd9..8c42aa807f 100644
--- a/libnetdata/circular_buffer/circular_buffer.h
+++ b/libnetdata/circular_buffer/circular_buffer.h
@@ -8,12 +8,12 @@ struct circular_buffer {
     char *data;
 };
 
-extern struct circular_buffer *cbuffer_new(size_t initial, size_t max);
-extern void cbuffer_free(struct circular_buffer *buf);
-extern int cbuffer_add_unsafe(struct circular_buffer *buf, const char *d, size_t d_len);
-extern void cbuffer_remove_unsafe(struct circular_buffer *buf, size_t num);
-extern size_t cbuffer_next_unsafe(struct circular_buffer *buf, char **start);
-extern size_t cbuffer_available_size_unsafe(struct circular_buffer *buf);
-extern void cbuffer_flush(struct circular_buffer*buf);
+struct circular_buffer *cbuffer_new(size_t initial, size_t max);
+void cbuffer_free(struct circular_buffer *buf);
+int cbuffer_add_unsafe(struct circular_buffer *buf, const char *d, size_t d_len);
+void cbuffer_remove_unsafe(struct circular_buffer *buf, size_t num);
+size_t cbuffer_next_unsafe(struct circular_buffer *buf, char **start);
+size_t cbuffer_available_size_unsafe(struct circular_buffer *buf);
+void cbuffer_flush(struct circular_buffer*buf);
 
 #endif