Add omemo_close function

We call omemo_init() when starting profanity and should have an
omemo_close() at exit.

For now we free the fingerprint autocompleter in there.

Fixes valgrind:
```
==13226== 24 bytes in 1 blocks are definitely lost in loss record 2,855
of 6,958
==13226==    at 0x483677F: malloc (in
/usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
==13226==    by 0x48AD39: autocomplete_new (autocomplete.c:57)
==13226==    by 0x4AB89F: omemo_init (omemo.c:127)
==13226==    by 0x42C283: _init (profanity.c:206)
==13226==    by 0x42BFF3: prof_run (profanity.c:98)
==13226==    by 0x4B25E6: main (main.c:172)
```

Regards https://github.com/profanity-im/profanity/issues/1131

1 files changed, 1 insertions, 0 deletions

diff --git a/src/omemo/omemo.h b/src/omemo/omemo.h
index ae25b5ba..abe21be5 100644
--- a/src/omemo/omemo.h
+++ b/src/omemo/omemo.h
@@ -56,6 +56,7 @@ typedef struct omemo_key {
 } omemo_key_t;
 
 void omemo_init(void);
+void omemo_close(void);
 void omemo_on_connect(ProfAccount *account);
 void omemo_on_disconnect(void);
 void omemo_generate_crypto_materials(ProfAccount *account);