Remove FieldExt::rand

This removes a dependency on the `getrandom` crate in no-std mode, which
doesn't work on some no-std targets that `getrandom` doesn't support.

CHANGELOG.md

@@ -21,6 +21,7 @@ and this project adheres to Rust's notion of
   - `FieldExt::from_u64` (use `From<u64> for ff::PrimeField` instead).
   - `FieldExt::{from_bytes, read, to_bytes, write}`
     (use `ff::PrimeField::{from_repr, to_repr}` instead).
+  - `FieldExt::rand` (use `ff::Field::random` instead).
 
 ## [0.2.1] - 2021-09-17
 ### Changed

Cargo.toml

@@ -44,7 +44,7 @@ required-features = ["std"]
 blake2b_simd = { version = "0.5", default-features = false }
 ff = { version = "0.11", default-features = false }
 group = { version = "0.11", default-features = false }
-rand = { version = "0.8", default-features = false, features = ["getrandom"] }
+rand = { version = "0.8", default-features = false }
 static_assertions = "1.1.0"
 subtle = { version = "2.3", default-features = false }
 

src/arithmetic/fields.rs

@@ -112,11 +112,6 @@ pub trait FieldExt: SqrtRatio + From<bool> + Ord + Group<Scalar = Self> {
     /// Element of multiplicative order $3$.
     const ZETA: Self;
 
-    /// This computes a random element of the field using system randomness.
-    fn rand() -> Self {
-        Self::random(rand::rngs::OsRng)
-    }
-
     /// Obtains a field element congruent to the integer `v`.
     fn from_u128(v: u128) -> Self;