Remove powi, "square can be computed more efficiently"

[mucinoab]

powi(2) produces exactly the same native code as x * x
powi was part of the [suboptimal_flops] lint

fixes #7058
changelog: Remove powi [suboptimal_flops], "square can be computed more efficiently"

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[giraffate]

Why does this case also removed?

[mucinoab]

It is just a special case for

rust-clippy/clippy_lints/src/floating_point_arithmetic.rs

Line 403 in c8d52e3

fn check_mul_add(cx: &LateContext<'_>, expr: &Expr<'_>) {

Should we keep it?

[giraffate]

In the related issue, I found that the case of x * x was discussed, but I couldn't find the discussion of mul_add. So I don't know why this case needs to be removed as same.

If there is no reason, I think it would be better to keep it.

[mucinoab]

@giraffate I did some changes. Should we keep the same names for everything?

[giraffate]

@mucinoab It looks good! Can you squash the commits and mark this PR as ready?

[mucinoab]

@giraffate All done.

[giraffate]

@bors r+

Thanks!

[bors]

📌 Commit be540e6 has been approved by giraffate

[bors]

⌛ Testing commit be540e6 with merge 9028173...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: giraffate
Pushing 9028173 to master...