Clean up the license field in various templates.

Created by: kacbuk001

Clean up the license field in various templates to ensure it's unlicense by default.

PR checklist

• [DONE] Read the contribution guidelines.
• [DONE] Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh, ./bin/openapi3/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\.
• [DONE] Filed the PR against the correct branch: master, 3.4.x, 4.0.x. Default: master.

Description of the PR

Changes based on the discussion contained in: https://github.com/OpenAPITools/openapi-generator/issues/2255

The following scripts was executed: bin/php-lumen-petstore-server.sh bin/php-ze-ph-petstore-server.sh bin/php-symfony-petstore.sh bin/openapi3/php-ze-ph-petstore-server.sh bin/openapi3/php-petstore.sh bin/php-petstore.sh bin/ruby-client-petstore.sh

The script associated with 'php-ze-ph' generated several new files. These areas where not modified by me, so I assume that the content of the 'sample' folder was not up to date.