all: move description of C files below the copyright and license

src/plugins/exec/exec-command.c

@@ -1,6 +1,4 @@
 /*
- * exec-command.c - exec command
- *
  * SPDX-FileCopyrightText: 2014-2025 Sébastien Helleu <flashcode@flashtux.org>
  *
  * SPDX-License-Identifier: GPL-3.0-or-later
@@ -21,6 +19,8 @@
  * along with WeeChat.  If not, see <https://www.gnu.org/licenses/>.
  */
 
+/* Exec command */
+
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>