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, 8 insertions, 8 deletions

diff --git a/libnetdata/string/string.h b/libnetdata/string/string.h
index f527f042ff..cec44ebd99 100644
--- a/libnetdata/string/string.h
+++ b/libnetdata/string/string.h
@@ -8,14 +8,14 @@
 // STRING implementation
 
 typedef struct netdata_string STRING;
-extern STRING *string_strdupz(const char *str);
-extern STRING *string_dup(STRING *string);
-extern void string_freez(STRING *string);
-extern size_t string_strlen(STRING *string);
-extern const char *string2str(STRING *string) NEVERNULL;
+STRING *string_strdupz(const char *str);
+STRING *string_dup(STRING *string);
+void string_freez(STRING *string);
+size_t string_strlen(STRING *string);
+const char *string2str(STRING *string) NEVERNULL;
 
 // keep common prefix/suffix and replace everything else with [x]
-extern STRING *string_2way_merge(STRING *a, STRING *b);
+STRING *string_2way_merge(STRING *a, STRING *b);
 
 static inline int string_cmp(STRING *s1, STRING *s2) {
     // STRINGs are deduplicated, so the same strings have the same pointer
@@ -23,8 +23,8 @@ static inline int string_cmp(STRING *s1, STRING *s2) {
     return (s1 == s2)?0:strcmp(string2str(s1), string2str(s2));
 }
 
-extern void string_statistics(size_t *inserts, size_t *deletes, size_t *searches, size_t *entries, size_t *references, size_t *memory, size_t *duplications, size_t *releases);
+void string_statistics(size_t *inserts, size_t *deletes, size_t *searches, size_t *entries, size_t *references, size_t *memory, size_t *duplications, size_t *releases);
 
-extern int string_unittest(size_t entries);
+int string_unittest(size_t entries);
 
 #endif