Global context is randomized twice

[DaniPopes]

In:

rust-secp256k1/src/context.rs

Lines 44 to 63 in bb4972f

	#[allow(unused_mut)] // Unused when `rand` + `std` is not enabled.
	fn deref(&self) -> &Self::Target {
	static ONCE: Once = Once::new();
	static mut CONTEXT: Option<Secp256k1<All>> = None;
	ONCE.call_once(|| unsafe {
	let mut ctx = Secp256k1::new();
	#[cfg(all(
	not(target_arch = "wasm32"),
	feature = "rand",
	feature = "std",
	not(feature = "global-context-less-secure")
	))]
	{
	ctx.randomize(&mut rand::thread_rng());
	}
	CONTEXT = Some(ctx);
	});
	unsafe { CONTEXT.as_ref().unwrap() }
	}
	}

Secp256k1::new itself calls randomize with rand:

rust-secp256k1/src/context.rs

Lines 206 to 234 in bb4972f

	pub fn gen_new() -> Secp256k1<C> {
	#[cfg(target_arch = "wasm32")]
	ffi::types::sanity_checks_for_wasm();
	let size = unsafe { ffi::secp256k1_context_preallocated_size(C::FLAGS) };
	let layout = alloc::Layout::from_size_align(size, ALIGN_TO).unwrap();
	let ptr = unsafe { alloc::alloc(layout) };
	let ptr = NonNull::new(ptr as *mut c_void)
	.unwrap_or_else(|| alloc::handle_alloc_error(layout));
	#[allow(unused_mut)] // ctx is not mutated under some feature combinations.
	let mut ctx = Secp256k1 {
	ctx: unsafe { ffi::secp256k1_context_preallocated_create(ptr, C::FLAGS) },
	phantom: PhantomData,
	};
	#[cfg(all(
	not(target_arch = "wasm32"),
	feature = "rand",
	feature = "std",
	not(feature = "global-context-less-secure")
	))]
	{
	ctx.randomize(&mut rand::thread_rng());
	}
	#[allow(clippy::let_and_return)] // as for unusted_mut
	ctx
	}

Is this intended? If not, the call in deref should be dropped.

[apoelstra]

Good catch. Yeah, let's drop the one in deref.

cc #388