Potentially redundant/upliftable lints

A few lints I noticed which may be redundant to newer lints in rustc upstream:

• absurd_extreme_comparisons should be uplifted to the existing unused_comparisons
• bad_bit_mask should probably be uplifted to the existing unused_comparisons lint, or an unused_bitmask lint
• bool_comparison should probably be uplifted to unused_comparisons
• cmp_nan should probably be again uplifted to unused_comparisons
• eq_op should probably be again uplifted to unused_comparisons
• unused_collect should be replaced by the existing must_use on collect
• useless_attribute should be replaced by unused_attribute
• out_of_bounds_indexing should be a const eval error
• iterator_step_by_zero should be removed; this now panics
• enum_clike_unportable_variant should be part of a compiler portability lint

(will make larger list when I get around to it)

Start with the ten lints listed in issue #2846 and compare each with its current rustc upstream or Clippy status. Done means reaching a decision for every listed lint—uplift, replacement, removal, or compiler portability handling—and documenting or implementing those decisions.