Remove or move localized string functions for accessibility.

Fold the following functions to callsites:
 - AXButtonActionVerb()
 - AXCheckedCheckBoxActionVerb()
 - AXLinkActionVerb()
 - AXMenuListActionVerb()
 - AXMenuListPopupActionVerb()
 - AXRadioButtonActionVerb()
 - AXTextFieldActionVerb()
 - AXUncheckedCheckBoxActionVerb()

And move unimplemented localizedMediaTimeDescription() to
AccessibilityMediaControls.cpp.

BUG=298020
TEST=none; no behavior changes.

Review URL: https://codereview.chromium.org/26445003

git-svn-id: svn://svn.chromium.org/blink/trunk@159307 bbb929c8-8fbe-4397-9dbb-9b2b20218538