Fix @metamask/eth-sig-util types (#248)

The types for the package `@metamask/eth-sig-util` were being
overwritten by a local type declaration. That has been removed, and all
type errors have been resolved.

All of the type errors were related to `normalize` returning
`undefined` if given a nullish input. We never pass it a nullish input,
but TypeScript wasn't able to infer that, so that issue was addressed
with type casts. This isn't ideal, but it's temporary. Once we finish
migrating all Keyrings to the new Keyring interface, we won't need to
normalize addresses anymore at all.

Author: Gudahtt

src/KeyringController.ts

@@ -334,7 +334,9 @@ class KeyringController extends EventEmitter {
       return res.concat(arr);
     }, []);
 
-    return addresses.map(normalizeToHex);
+    // Cast to `Hex[]` here is safe here because `addresses` has no nullish
+    // values, and `normalizeToHex` returns `Hex` unless given a nullish value
+    return addresses.map(normalizeToHex) as Hex[];
   }
 
   /**
@@ -515,7 +517,9 @@ class KeyringController extends EventEmitter {
     },
     opts: Record<string, unknown> = { version: 'V1' },
   ): Promise<Bytes> {
-    const address = normalizeToHex(msgParams.from);
+    // Cast to `Hex` here is safe here because `msgParams.from` is not nullish.
+    // `normalizeToHex` returns `Hex` unless given a nullish value.
+    const address = normalizeToHex(msgParams.from) as Hex;
     const keyring = await this.getKeyringForAccount(address);
     if (!keyring.signTypedData) {
       throw new Error(KeyringControllerError.UnsupportedSignTypedMessage);
@@ -697,7 +701,9 @@ class KeyringController extends EventEmitter {
    * @returns The keyring of the account, if it exists.
    */
   async getKeyringForAccount(address: string): Promise<Keyring<Json>> {
-    const hexed = normalizeToHex(address);
+    // Cast to `Hex` here is safe here because `address` is not nullish.
+    // `normalizeToHex` returns `Hex` unless given a nullish value.
+    const hexed = normalizeToHex(address) as Hex;
 
     const candidates = await Promise.all(
       this.keyrings.map(async (keyring) => {
@@ -1086,7 +1092,9 @@ async function displayForKeyring(
 
   return {
     type: keyring.type,
-    accounts: accounts.map(normalizeToHex),
+    // Cast to `Hex[]` here is safe here because `addresses` has no nullish
+    // values, and `normalizeToHex` returns `Hex` unless given a nullish value
+    accounts: accounts.map(normalizeToHex) as Hex[],
   };
 }