Remove M5Timer

[ikedam]

• It's licensed under LGPL2.1+.
  • See Software license issue #21 for more details about the license issue.
• It's not documented.
  • The only document I reached is https://github.com/m5stack/m5-docs/blob/master/docs/en/api/M5Timer.md . But it's only in English and not linked from other pages.

I think I can re-implement it from scratch referring the documentation above. Please let me know if this feature should be continue to provide.

[Gitshaoxiang]

I think we don't need re-implement it. for the time being, we don't have to use it. when people need it, they could download it from the source project github. so I think we don't need to include a timer function in the EPD lib