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/src/panic.c b/src/panic.c
index e233588..251fdad 100644
--- a/src/panic.c
+++ b/src/panic.c
@@ -25,7 +25,7 @@
  */
 
 /*! \file panic.c
- *  \brief Routines for panic handling
+ *  Routines for panic handling
  */
 
 #include <osmocom/core/panic.h>
@@ -59,7 +59,7 @@
 #endif
 
 
-/*! \brief Terminate the current program with a panic
+/*! Terminate the current program with a panic
  *
  * You can call this function in case some severely unexpected situation
  * is detected and the program is supposed to terminate in a way that
@@ -87,7 +87,7 @@
 }
  
 
-/*! \brief Set the panic handler
+/*! Set the panic handler
  *  \param[in] h New panic handler function
  *
  *  This changes the panic handling function from the currently active