Improve detection of system tray support

Closes #2045

src/common/util.h

@@ -76,7 +76,6 @@ guint32 str_ihash (const unsigned char *key);
 void safe_strcpy (char *dest, const char *src, int bytes_left);
 void canonalize_key (char *key);
 int portable_mode (void);
-int unity_mode (void);
 char *encode_sasl_pass_plain (char *user, char *pass);
 char *challengeauth_response (const char *username, const char *password, const char *challenge);
 size_t strftime_validated (char *dest, size_t destsize, const char *format, const struct tm *time);