Revert "Initialize LayoutTableCell.is_spanning_collapsed_row_ to avoid MSAN error"

This reverts commit b25f768c.

Reason for revert: Caused compile error.

https://luci-logdog.appspot.com/v/?s=chromium%2Fbb%2Fchromium.webkit%2FWebKit_Mac_Builder__dbg_%2F209280%2F%2B%2Frecipes%2Fsteps%2Fcompile%2F0%2Fstdout

../../third_party/WebKit/Source/core/layout/LayoutTableCell.cpp:63:7: error: member initializer 'is_spanning_collapsed_row_' does not name a non-static data member or base class
      is_spanning_collapsed_row_(false),
      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.

Original change's description:
> Initialize LayoutTableCell.is_spanning_collapsed_row_ to avoid MSAN error
> 
> TBR: joysyu@google.com
> Bug: 751407
> Change-Id: I3bb805d6f6c2a555925ce3ccf514e1e4b2d8df0a
> Reviewed-on: https://chromium-review.googlesource.com/597031
> Reviewed-by: Tsuyoshi Horo <horo@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#491295}

TBR=horo@chromium.org,joysyu@google.com

Change-Id: Ice425494d4c1de47a48497636401616d9fe6cc89
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 751407
Reviewed-on: https://chromium-review.googlesource.com/597093Reviewed-by: Tsuyoshi Horo <horo@chromium.org>
Commit-Queue: Tsuyoshi Horo <horo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#491318}

third_party/WebKit/Source/core/layout/LayoutTableCell.cpp

@@ -60,7 +60,6 @@ LayoutTableCell::LayoutTableCell(Element* element)
     : LayoutBlockFlow(element),
       absolute_column_index_(kUnsetColumnIndex),
       cell_width_changed_(false),
-      is_spanning_collapsed_row_(false),
       collapsed_border_values_valid_(false),
       intrinsic_padding_before_(0),
       intrinsic_padding_after_(0) {