qerror: QERR_QGA_COMMAND_FAILED is no longer used, drop

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-ID: <20240514105829.729342-4-armbru@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Konstantin Kostiuk <kkostiuk@redhat.com>

include/qapi/qmp/qerror.h

@@ -26,9 +26,6 @@
 #define QERR_PROPERTY_VALUE_OUT_OF_RANGE \
     "Property %s.%s doesn't take value %" PRId64 " (minimum: %" PRId64 ", maximum: %" PRId64 ")"
 
-#define QERR_QGA_COMMAND_FAILED \
-    "Guest agent command failed, error was '%s'"
-
 #define QERR_UNSUPPORTED \
     "this feature or command is not currently supported"