webdriver: Synchronize "close window" command & Return correct error type (#38620)

1. Synchronize [Close
Window](https://w3c.github.io/webdriver/#dfn-close-window) command to
reduce intermittency
2. There was a update last month exposing that we are not returning
correct error type for Session getter.
https://github.com/web-platform-tests/wpt/pull/53735
3. Other trivial fix

Testing: 
- `/webdriver/tests/classic/close_window/close.py` can now fully pass.
- `/webdriver/tests/classic/delete_session/*` can now fully pass.

---------

Signed-off-by: Euclid Ye <euclid.ye@huawei.com>

tests/wpt/meta/webdriver/tests/classic/close_window/close.py.ini

@@ -1,3 +0,0 @@
-[close.py]
-  [test_close_last_browsing_context]
-    expected: FAIL

tests/wpt/meta/webdriver/tests/classic/delete_session/delete.py.ini

@@ -1,3 +0,0 @@
-[delete.py]
-  [test_accepted_beforeunload_prompt]
-    expected: FAIL