Remove exception logging to reduce test noise

A WebDriverException is frequently raised under normal use of these
classes, for example in `text_to_equal()` when the element is not yet
part of the page.

Example exceptions:

```
ERROR    dash.testing.wait:wait.py:95 text_to_equal encountered an exception
Traceback (most recent call last):
  File "/home/circleci/dds/venv/lib/python3.6/site-packages/dash/testing/wait.py", line 91, in __call__
    str(elem.text) == self.text
  File "/home/circleci/dds/venv/lib/python3.6/site-packages/selenium/webdriver/remote/webelement.py", line 76, in text
    return self._execute(Command.GET_ELEMENT_TEXT)['value']
  File "/home/circleci/dds/venv/lib/python3.6/site-packages/selenium/webdriver/remote/webelement.py", line 633, in _execute
    return self._parent.execute(command, params)
  File "/home/circleci/dds/venv/lib/python3.6/site-packages/selenium/webdriver/remote/webdriver.py", line 321, in execute
    self.error_handler.check_response(response)
  File "/home/circleci/dds/venv/lib/python3.6/site-packages/selenium/webdriver/remote/errorhandler.py", line 242, in check_response
    raise exception_class(message, screen, stacktrace)
selenium.common.exceptions.StaleElementReferenceException: Message: stale element reference: element is not attached to the page document
  (Session info: chrome=80.0.3987.132)
```

```
ERROR    dash.testing.wait:wait.py:85 text_to_equal encountered an exception
Traceback (most recent call last):
  File "/home/circleci/dds/venv/lib/python3.6/site-packages/dash/testing/wait.py", line 78, in __call__
    elem = driver.find_element_by_css_selector(self.selector)
  File "/home/circleci/dds/venv/lib/python3.6/site-packages/selenium/webdriver/remote/webdriver.py", line 598, in find_element_by_css_selector
    return self.find_element(by=By.CSS_SELECTOR, value=css_selector)
  File "/home/circleci/dds/venv/lib/python3.6/site-packages/selenium/webdriver/remote/webdriver.py", line 978, in find_element
    'value': value})['value']
  File "/home/circleci/dds/venv/lib/python3.6/site-packages/selenium/webdriver/remote/webdriver.py", line 321, in execute
    self.error_handler.check_response(response)
  File "/home/circleci/dds/venv/lib/python3.6/site-packages/selenium/webdriver/remote/errorhandler.py", line 242, in check_response
    raise exception_class(message, screen, stacktrace)
selenium.common.exceptions.NoSuchElementException: Message: no such element: Unable to locate element: {"method":"css selector","selector":"h1"}
  (Session info: chrome=80.0.3987.163)
```

Author: Jody McIntyre

dash/testing/wait.py

@@ -64,7 +64,6 @@ def __call__(self, driver):
                 elem.get_attribute("value")
             )
         except WebDriverException:
-            logger.exception("contains_text encountered an exception")
             return False
 
 
@@ -82,7 +81,6 @@ def __call__(self, driver):
                 or str(elem.get_attribute("value")) == self.text
             )
         except WebDriverException:
-            logger.exception("text_to_equal encountered an exception")
             return False
 
 
@@ -99,5 +97,4 @@ def __call__(self, driver):
             logger.debug("style to equal {%s} => expected %s", val, self.val)
             return val == self.val
         except WebDriverException:
-            logger.exception("style_to_equal encountered an exception")
             return False