Remove pre-commit in Dev Container and fix a format script

[yutaro-sakamoto]

This pull request primarily focuses on removing the pre-commit hook setup and updating the documentation to reflect these changes. Additionally, this pull request removes the pplex.c file from the list of source files in format.

Removal of pre-commit hook setup:

• .devcontainer/boot.sh: Removed the setup of the pre-commit hook from the boot script.
• .devcontainer/term_settings/pre-commit: Deleted the pre-commit hook script that formatted code and staged changes. It is up to each developer to decide whether to use pre-commit.

Documentation updates:

• CONTRIBUTING.md: Removed the section about Git Hooks executing code formatters during the git commit command and updated instructions to manually run ./format before committing or submitting pull requests.
• CONTRIBUTING_JP.md: Similar updates as CONTRIBUTING.md, removing the Git Hooks section and advising manual execution of ./format.

Minor codebase adjustment:

• cobj/format: Removed the pplex.c file from the list of source files.
  • It is not import to check the format of pplec.c because flex automatically generates it.
  • In the past, the formatter accidentally updates pplex.c.
    • https://github.com/opensourcecobol/opensourcecobol4j/pull/545/files