chore: minor cleanup mode_t usage

[nyurik]

crate::mode_t is almost never needed because it is part of prelude. Moreover, in many cases mode_t was already used without the prefix - thus confusing if they are different or not. Keeping it the same helps readability.

@rustbot label +stable-nominated

[rustbot]

r? @tgross35

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[rustbot]

Some changes occurred in OpenBSD module

cc @semarie

Some changes occurred in OpenBSD module

cc @semarie

Some changes occurred in the Android module

cc @maurer

Some changes occurred in solarish module

cc @jclulow, @pfmooney

[tgross35]

Thanks!