version_name is an invalid manifest key

[machawk1]

Based off of https://developer.mozilla.org/en-US/Add-ons/WebExtensions/API/management/ExtensionInfo, our usage of version_name in the manifest to distinguish builds, a change or removal of this attribute is needed to be compatible with WebExtensions.

Removal is not critical, as the field will likely be ignored. Firefox's more expressive version value would normally be a good replacement exception it is more expressive than Chrome allows for this field, so information like "build" is not allowed in the version string for Chrome.