hw/sd: Remove unused 'enable' method from SDCardClass

hw/sd: Remove unused 'enable' method from SDCardClass

The SDCardClass has an 'enable' method, but nothing actually invokes it.
The underlying implementation is sd_enable(), which is documented
in sdcard_legacy.h as something that should not be used and was only
present for the benefit of the now-removed nseries boards. Unlike
all the other method pointers in SDCardClass, this one doesn't have
an sdbus_foo() function wrapper in hw/sd/core.c.

Remove the unused method.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20250128104519.3981448-10-peter.maydell@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>