This commit fixes the UserError message by properly displaying the
number of maximum leads that can be merged.
Apart from that, this commit also hides 'email_from' and 'phone' fields
on merge wizard to avoid scroll and to make sure that the 'x' icon is
always visible, which previously was far right and user had to scroll
a bit for removing the lines with that button.
TaskID-2542260
closesodoo/odoo#71523
X-original-commit: abbf3419767c149f338a4a48f15c2af7dfbed2bc
Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>