doxygen: enable AUTOBRIEF, drop \brief

Especially for short descriptions, it is annoying to have to type \brief for
every single API doc.

Drop all \brief and enable the AUTOBRIEF feature of doxygen, which always takes
the first sentence of an API doc as the brief description.

Change-Id: I11a8a821b065a128108641a2a63fb5a2b1916e87
diff --git a/include/osmocom/gsm/gsm_utils.h b/include/osmocom/gsm/gsm_utils.h
index 1ffe579..e76d9ee 100644
--- a/include/osmocom/gsm/gsm_utils.h
+++ b/include/osmocom/gsm/gsm_utils.h
@@ -60,7 +60,7 @@
 enum gsm_band gsm_band_parse(const char *mhz);
 
 /*!
- * \brief Decode a sequence of GSM 03.38 encoded 7 bit characters.
+ * Decode a sequence of GSM 03.38 encoded 7 bit characters.
  *
  * \param decoded	The destination buffer for the decoded characters.
  * \param n		A maximum of n chars is written (incl. terminating \0).
@@ -76,14 +76,14 @@
 int gsm_7bit_decode_n(char *decoded, size_t n, const uint8_t *user_data, uint8_t length);
 
 /*!
- * \brief Decode a sequence of 7 bit characters (USSD encoding).
+ * Decode a sequence of 7 bit characters (USSD encoding).
  *
  * \see gsm_7bit_encode_n()
  */
 int gsm_7bit_decode_n_ussd(char *decoded, size_t n, const uint8_t *user_data, uint8_t length);
 
 /*!
- * \brief Encode a text string into GSM 03.38 encoded 7 bit characters.
+ * Encode a text string into GSM 03.38 encoded 7 bit characters.
  *
  * \param result	The destination buffer for the packed 7 bit sequence.
  * \param n		A maximum of n octets is written.
@@ -97,7 +97,7 @@
 int gsm_7bit_encode_n(uint8_t *result, size_t n, const char *data, int *octets_written);
 
 /*!
- * \brief Encode a text string into GSM 03.38 encoded 7 bit characters (USSD encoding).
+ * Encode a text string into GSM 03.38 encoded 7 bit characters (USSD encoding).
  *
  * \see gsm_7bit_decode_n()
  */