Fix issue with change-tracked deleted display math

Fix issue with change-tracked deleted display math

- If a display math not starting a new paragraph is deleted, the
  current \lyxdeleted macro (if any) must be closed and a new one
  started, otherwise the display math will be shifted up.

- Use \linewidth instead of \columnwidth because the former will adapt
  to the reduced horizontal width in list environments, avoiding shifting
  to the right the diplay math.

(cherry picked from commit 7f23ca912c5e92bf30bdc05b6d801082f6643e8e)