Fix #5795 - Error page not shown on reload

[garvankeeley]

The old reload logic was to use a timestamp to determine if the error
page was being loaded or reloaded. The idea was that if errorpage load
was called with a timestamped URL <2s, load the errorpage html file; if
errorpage load was called with a timestamped URL >2s old then reload the
original page. It allowed for one codepath to handle the load/reload logic,
but it is very flaky.
Instead just have the reload buttons have special behaviour to reload
the original URL.

[mozillamobilebot]

SwiftLint found issues

Warnings

File	Line	Reason
Tab.swift	192	Colons should be next to the identifier when specifying a type and next to the key in dictionary literals. (colon)
Tab.swift	368	Prefer empty collection over optional collection. (discouraged_optional_collection)
Tab.swift	372	Prefer empty collection over optional collection. (discouraged_optional_collection)
Tab.swift	566	Prefer empty collection over optional collection. (discouraged_optional_collection)
Tab.swift	257	Limit vertical whitespace to a single empty line. Currently 2. (vertical_whitespace)

Errors

File	Line	Reason
Tab.swift	401	There should be no space before and one after any comma. (comma)

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