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/coding/gsm0503_coding.h b/include/osmocom/coding/gsm0503_coding.h
index 2f0e631..a9c59e4 100644
--- a/include/osmocom/coding/gsm0503_coding.h
+++ b/include/osmocom/coding/gsm0503_coding.h
@@ -8,7 +8,7 @@
  */
 
 /*! \file gsm0503_coding.h
- *  \brief GSM TS 05.03 coding
+ *  GSM TS 05.03 coding
  */
 
 #define GSM0503_GPRS_BURSTS_NBITS	(116 * 4)