[FIX] web_editor: avoid vertical dropzones from taking too much space

[bso-odoo]

Since 1 when BS5 was introduced, vertical dropzones sometime push row elements to the next row.

This commit removes the padding on the vertical dropzones, that is introduced on rows by BS5.

task-2993565

Description of the issue/feature this PR addresses:

Current behavior before PR:

Desired behavior after PR is merged:

-- I confirm I have signed the CLA and read the PR guidelines at www.odoo.com/submit-pr

[robodoo]

[bso-odoo]

@qsm-odoo The BS5 rows have padding that did not exist on BS4 rows.