Remove the legacy blame ?page= query param

What does this MR do and why?

This MR is one of in the series related to #618439 (closed).

This MR removes the legacy blame ?page= query param and its supporting code.

The param only ever addressed the paginated legacy blame page, and neither call site ever actually produced one. chunk.vue passed this.number, which was declared undefined in data() and never assigned, while getAbsolutePermalinkPath passed a hash string like #L6 for which parseInt('#L6', 10) is NaN, so both fall through to the empty string. The helper only works when handed a bare integer, which nothing does, and the existing specs hid this by stubbing getPageParamValue to return '2'.

References

• #618439 (closed) (Follow-up issue: Remove the legacy Blame page)
• !257407 (merged) (Dependency MR: Remove inline_blame feature flag)
• !257919 (merged) (Sibling MR B: Retire the legacy blame page actions and routes)
• !257920 (merged) (Sibling MR C: Remove dead legacy blame frontend entrypoints)

These three MRs touch no files in common and can be reviewed in parallel.

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