Run (most) common tests against the custom RNG

Signed-off-by: Joe Richey <joerichey@google.com>

tests/common/mod.rs

@@ -13,6 +13,7 @@ fn test_zero() {
 }
 
 #[test]
+#[cfg(not(feature = "custom"))]
 fn test_diff() {
     let mut v1 = [0u8; 1000];
     getrandom_impl(&mut v1).unwrap();

tests/custom.rs

@@ -7,8 +7,6 @@
 ))]
 
 use wasm_bindgen_test::wasm_bindgen_test as test;
-#[cfg(feature = "test-in-browser")]
-wasm_bindgen_test::wasm_bindgen_test_configure!(run_in_browser);
 
 use core::num::NonZeroU32;
 use getrandom::{getrandom, register_custom_getrandom, Error};
@@ -33,6 +31,9 @@ fn super_insecure_rng(buf: &mut [u8]) -> Result<(), Error> {
 
 register_custom_getrandom!(super_insecure_rng);
 
+use getrandom::getrandom as getrandom_impl;
+mod common;
+
 #[test]
 fn custom_rng_output() {
     let mut buf = [0u8; 4];