Revert "[MVT Customization] Add and use TilesLinearLayout."

This reverts commit d1ea2a0b25d4e4c30e921f90d42cea70cded170b.

Reason for revert: Failure in org.chromium.chrome.browser.ntp.NewTabPageTest#testMvtContainerOnNtp on tablet shows that this CL is not a pure refactoring; will return to this issue later.

Original change's description:
> [MVT Customization] Add and use TilesLinearLayout.
>
> For MVT Customization we'd like to render a divider between Custom Tiles
> and Top-Sites Tiles. The addition conflicts with the previous assumption
> that MostVisitedTilesLayout's children consist of SuggestionsTileView,
> as seen by getChildCount() and getChildAt() usages to:
> * Cache tiles for reuse when re-rendering.
> * Dynamically tweak margins to adjust tile spacing.
>
> This is a refactoring CL that mostly updates MostVisitedTilesLayout:
> * Prepare for the addition of tile dividers.
> * Update tablet edge margins computation, so that the UI decision to
>   avoid changing from scrollable container -> centered container
>   becomes more explicit.
>
> Details:
> * Add TilesLinearLayout, to be inserted in inheritance chain via
>   LinearLayout <- TilesLinearLayout <- MostVisitedTilesLayout:
>   * Field |mTileList| to store a List<TileView>.
>   * Methods: {addTile(), getTileCount(), getTileAt()} to replace
>     {addView(), getChildCount(), getChildAt()} for tiles.
>   * Note: Storing TileView instead of SuggestionsTileView, since this is
>     needed by some tests.
>   * Override: removeAllViews() to clear |mTileList|.
> * MostVisitedTilesLayout:
>   * Dimension fields: Use DP where applicable, since it's better to add
>     DP sizes before converting to PX, instead of converting first.
>     * Add "Dp" or "Px" suffixes wherever applicable.
>   * updateSingleViewStartMargin(), updateSingleViewEndMargin(): Relace
>     param from TileView to View, to prepare for dividers.
>   * Extract computeContentWidthPx() (with better DP usage)
>   * Extract edge padding computation computeEdgePaddingPx(), simplifying
>     the logic while adding comments.
>     * Replace |mInitialTileNum| with |mInitialContentWidthPx|.
>   * updateEdgeMarginTablet(): Reduce to use the above.
> * General:
>   * Replace ViewGroup / LinearLayout usages intended for parent to
>     TilesLinearLayout.
>   * Change {getChildCount(), getChildAt()} to {getTileCount(),
>     getTileAt()} wherever applicable.
>
> Bug: 400481269, 388782412
> Change-Id: I3388767d9fa81df88d727d972b0366416589dce0
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6324689
> Reviewed-by: Calder Kitagawa <ckitagawa@chromium.org>
> Reviewed-by: Xinyi Ji <xinyiji@chromium.org>
> Commit-Queue: Samuel Huang <huangs@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1430330}

Bug: 400481269, 388782412
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Change-Id: Iec179699a78fc9217aaf32f93b14f60876ca43d1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6342572
Reviewed-by: Calder Kitagawa <ckitagawa@chromium.org>
Auto-Submit: Samuel Huang <huangs@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Calder Kitagawa <ckitagawa@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1430766}