libsysprof-capture: Stop defining G_LOG_DOMAIN

libsysprof-capture no longer calls any of the GLib logging functions
which make use of it.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

Helps: #40

src/libsysprof-capture/mapped-ring-buffer.c

@@ -18,8 +18,6 @@
  * SPDX-License-Identifier: GPL-3.0-or-later
  */
 
-#define G_LOG_DOMAIN "mapped-ring-buffer"
-
 #include "config.h"
 
 #include <assert.h>