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/backtrace.c b/src/backtrace.c
index 6cd798c..0240a75 100644
--- a/src/backtrace.c
+++ b/src/backtrace.c
@@ -21,7 +21,7 @@
  */
 
 /*! \file backtrace.c
- *  \brief Routines realted to generating call back traces
+ *  Routines realted to generating call back traces
  */
 
 #include <stdio.h>
@@ -60,7 +60,7 @@
 	free(strings);
 }
 
-/*! \brief Generate and print a call back-trace
+/*! Generate and print a call back-trace
  *
  * This function will generate a function call back-trace of the
  * current process and print it to stdout. */
@@ -69,7 +69,7 @@
 	_osmo_backtrace(1, 0, 0);
 }
 
-/*! \brief Generate and log a call back-trace
+/*! Generate and log a call back-trace
  *  \param[in] subsys Logging sub-system
  *  \param[in] level Logging level
  *