virbuftest: remove extra G_GNUC_UNUSED markers

These functions do use the opaque argument.
Signed-off-by: NJán Tomko <jtomko@redhat.com>
Reviewed-by: NErik Skultety <eskultet@redhat.com>

tests/virbuftest.c

@@ -244,7 +244,7 @@ struct testBufAddStrData {
 };
 
 static int
-testBufAddStr(const void *opaque G_GNUC_UNUSED)
+testBufAddStr(const void *opaque)
 {
     const struct testBufAddStrData *data = opaque;
     virBuffer buf = VIR_BUFFER_INITIALIZER;
@@ -277,7 +277,7 @@ testBufAddStr(const void *opaque G_GNUC_UNUSED)
 
 
 static int
-testBufEscapeStr(const void *opaque G_GNUC_UNUSED)
+testBufEscapeStr(const void *opaque)
 {
     const struct testBufAddStrData *data = opaque;
     virBuffer buf = VIR_BUFFER_INITIALIZER;