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/core/timer.h b/include/osmocom/core/timer.h
index 48e7d8d..28785db 100644
--- a/include/osmocom/core/timer.h
+++ b/include/osmocom/core/timer.h
@@ -23,7 +23,7 @@
  */
 
 /*! \file timer.h
- *  \brief Osmocom timer handling routines
+ *  Osmocom timer handling routines
  */
 
 #pragma once
@@ -50,15 +50,15 @@
  *        remove the timers.
  *
  */
-/*! \brief A structure representing a single instance of a timer */
+/*! A structure representing a single instance of a timer */
 struct osmo_timer_list {
-	struct rb_node node;	  /*!< \brief rb-tree node header */
-	struct llist_head list;   /*!< \brief internal list header */
-	struct timeval timeout;   /*!< \brief expiration time */
-	unsigned int active  : 1; /*!< \brief is it active? */
+	struct rb_node node;	  /*!< rb-tree node header */
+	struct llist_head list;   /*!< internal list header */
+	struct timeval timeout;   /*!< expiration time */
+	unsigned int active  : 1; /*!< is it active? */
 
-	void (*cb)(void*);	  /*!< \brief call-back called at timeout */
-	void *data;		  /*!< \brief user data for callback */
+	void (*cb)(void*);	  /*!< call-back called at timeout */
+	void *data;		  /*!< user data for callback */
 };
 
 /**