[IMP] remove string attribute in tree view

[xaviedoanhduy]

• supersedes: [ADD] remove string attribute in tree view #78

• an example when migrating crm_phone

~/code/oca/odoo-module-migrator$  python -m odoo_module_migrate -d /home/trobz/code/oca/connector-telephony/16.0 -m crm_phone -i 10.0 -t 16.0
15:43:50   INFO        Run pre-commit
15:43:50   INFO        Stage and commit changes done by pre-commit
On branch 10.0
Your branch is up to date with 'origin/10.0'.

nothing to commit, working tree clean
15:43:50   INFO        [crm_phone] Running migration from 10.0 to 16.0
15:43:50   INFO        Change file content of crm_phonecall.xml
15:43:50   INFO        Bump version to 16.0.1.0.0
15:43:50   INFO        Change file content of __init__.py
15:43:50   INFO        Change file content of __manifest__.py
15:43:51   INFO        Commit changes for crm_phone. commit name '[MIG] crm_phone: Migration to 16.0'

[OCA-git-bot]

This PR has the approved label and has been created more than 5 days ago. It should therefore be ready to merge by a maintainer (or a PSC member if the concerned addon has no declared maintainer). 🤖