remove unnecessary use statement

Author: Goose

src/distribution/exponential.rs

@@ -301,8 +301,6 @@ impl Continuous<f64, f64> for Exp {
 #[rustfmt::skip]
 #[cfg(test)]
 mod tests {
-    use core::f64;
-
     use super::*;
     use crate::distribution::internal::density_util;
     use crate::distribution::internal::testing_boiler;