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/gsm/gea.c b/src/gsm/gea.c
index 8d026a2..d4e599c 100644
--- a/src/gsm/gea.c
+++ b/src/gsm/gea.c
@@ -37,7 +37,7 @@
 /*! \file gsm/gea.c */
 
 
-/*! \brief Performs the GEA4 algorithm as in 3GPP TS 55.226 V9.0.0
+/*! Performs the GEA4 algorithm as in 3GPP TS 55.226 V9.0.0
  *  \param[in,out] out Buffer for gamma for encrypted/decrypted
  *  \param[in] len Length of out, in bytes
  *  \param[in] kc Buffer with the ciphering key
@@ -51,7 +51,7 @@
 	return 0;
 }
 
-/*! \brief Performs the GEA3 algorithm as in 3GPP TS 55.216 V6.2.0
+/*! Performs the GEA3 algorithm as in 3GPP TS 55.216 V6.2.0
  *  \param[in,out] out Buffer for gamma for encrypted/decrypted
  *  \param[in] len Length of out, in bytes
  *  \param[in] kc Buffer with the ciphering key