core: deprecate gpiod_needs_update()

core: deprecate gpiod_needs_update()

This function and the logic behind have been introduced in an early
version of libgpiod for reasons that have been long forgotten.

When updating the line info after a line request fails, just propagate
the error out of the request function instead of setting the internal
needs_update variable. Drop the entire logic behind gpiod_needs_update(),
make this routine always return false and mark it as deprecated in the
header.

Suggested-by: Kent Gibson <warthog618@gmail.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>