bug#45915: 27.1; deletechar distorts org-table

[Tak Kunihiro]

I am using emacs 27.1 with orgtbl-mode.  On certain condition, typing
<deletechar> distorts alighment of a table.  Then, typing <up> moves
previous line but far right position.

|   | rownames |     |   | rownames |
| / | <l>      |     | / | <l>      |
|---+----------| ->  |---+----------|
| / | a        |     |  | a        |

Here is a recipe to reproduce the glitch started from emcas -Q.  I
hope that together with bug#45091, this would be fixed before 27.2.

1. Create a buffer with (text-mode) and yank following table.

|   | rownames |
| / | <l>      |
|---+----------|
|   | a        |

2. (progn (require 'org) (call-interactively 'orgtbl-mode))
3. Move point to the first column and the third line with letter 'a'.
4. Hit <S-return>.
5. Hit <deletechar>.
6. Hit <up>.