fix: drop undeclared err check and compare BigInt via Number in napi/create-int64

The @example block and README C example referenced an err variable
that stdlib_napi_create_int64 never produces; the native test also
compared the returned BigInt to a Number via strictEqual.

Author: claude

lib/node_modules/@stdlib/napi/create-int64/README.md

@@ -119,10 +119,6 @@ static napi_value addon( napi_env env, napi_callback_info info ) {
     napi_value value;
     napi_status status = stdlib_napi_create_int64( env, 1, &value );
     assert( status == napi_ok );
-    if ( err != NULL ) {
-        assert( napi_throw( env, err ) == napi_ok );
-        return NULL;
-    }
 
     // ...
 }

lib/node_modules/@stdlib/napi/create-int64/src/main.c

@@ -40,10 +40,6 @@
 *     napi_value value;
 *     napi_status status = stdlib_napi_create_int64( env, 1, &value );
 *     assert( status == napi_ok );
-*     if ( err != NULL ) {
-*         assert( napi_throw( env, err ) == napi_ok );
-*         return NULL;
-*     }
 *
 *     // ...
 * }

lib/node_modules/@stdlib/napi/create-int64/test/test.native.js

@@ -22,6 +22,7 @@
 
 var resolve = require( 'path' ).resolve;
 var tape = require( 'tape' );
+var Number = require( '@stdlib/number/ctor' );
 var tryRequire = require( '@stdlib/utils/try-require' );
 
 
@@ -78,7 +79,7 @@ tape( 'the function does not throw an error if provided a number', opts, functio
 	];
 	for ( i = 0; i < values.length; i++ ) {
 		v = addon( values[ i ] );
-		t.strictEqual( v, values[ i ], 'returns expected value when provided '+values[ i ] );
+		t.strictEqual( Number( v ), values[ i ], 'returns expected value when provided '+values[ i ] );
 	}
 	t.end();
 });