webnn: allow negative alpha value for elu operator

This CL removes the restriction of alpha value for elu operator
according to the discussion of this spec issue[1].

[1]:  webmachinelearning/webnn#383

Bug: 382108345
Change-Id: I78429de7630a37e71bdfc0fdacedde6e1c7d3879
Cq-Include-Trybots: luci.chromium.try:mac14.arm64-blink-rel, mac14-blink-rel, mac15.arm64-blink-rel, mac15-blink-rel, linux-blink-rel
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6081404
Reviewed-by: Austin Sullivan <asully@chromium.org>
Commit-Queue: Lisha Guo <lisha.guo@intel.com>
Reviewed-by: ningxin hu <ningxin.hu@intel.com>
Cr-Commit-Position: refs/heads/main@{#1396572}

webnn/validation_tests/elu.https.any.js

@@ -23,26 +23,6 @@ promise_test(async t => {
   assert_array_equals(output.shape, [1, 2, 3]);
 }, '[elu] Build with options');
 
-promise_test(async t => {
-  const builder = new MLGraphBuilder(context);
-  const options = {
-    alpha: -1.0,
-    label: label,
-  };
-  const input = builder.input('input', {dataType: 'float32', shape: [1, 2, 3]});
-  assert_throws_with_label(() => builder.elu(input, options), regrexp);
-}, '[elu] Throw if options.alpha < 0');
-
-promise_test(async t => {
-  const builder = new MLGraphBuilder(context);
-  const options = {
-    alpha: 0,
-    label: label,
-  };
-  const input = builder.input('input', {dataType: 'float32', shape: [1]});
-  assert_throws_with_label(() => builder.elu(input, options), regrexp);
-}, '[elu] Throw if options.alpha == 0');
-
 promise_test(async t => {
   const builder = new MLGraphBuilder(context);
   const options = {alpha: NaN};