doxygen: remove a few @file parameters.

It is not mandatory and prevents breakage on rename.

libavcodec/flashsv2enc.c

@@ -20,7 +20,7 @@
  */
 
 /**
- * @file libavcodec/flashsv2enc.c
+ * @file
  * Flash Screen Video Version 2 encoder
  * @author Joshua Warner
  */

libavcodec/msvideo1enc.c

@@ -20,7 +20,7 @@
  */
 
 /**
- * @file msvideo1enc.c
+ * @file
  * Microsoft Video-1 encoder
  */
 

libavfilter/transform.c

@@ -20,7 +20,7 @@
  */
 
 /**
- * @file libavfilter/transform.c
+ * @file
  * transform input video
  */
 

libavfilter/transform.h

@@ -20,7 +20,7 @@
  */
 
 /**
- * @file libavfilter/transform.h
+ * @file
  * transform input video
  *
  * All matrices are defined as a single 9-item block of contiguous memory. For

libavfilter/vf_deshake.c

@@ -20,7 +20,7 @@
  */
 
 /**
- * @file libavfilter/vf_deshake.c
+ * @file
  * fast deshake / depan video filter
  *
  * SAD block-matching motion compensation to fix small changes in