chore: remove unused devcontainer and gitpod configs

[yusukebe]

In this PR, I remove two things:

• .gitpod.yml - Anyone does not use this now.
• .devcontainer - I don't know if there is someone to use this. But keeping this has a small risk of attacks. It will be a rare case, but if an attacker adds malicious code into the container and it fires on the maintainer's machine, it will be bad.

And this is based on the policy - less is safe. As long as nothing is added, the project will be safer against supply chain attacks.

The author should do the following, if applicable

• Add tests
• Run tests
• bun run format:fix && bun run lint:fix to format the code
• Add TSDoc/JSDoc to document the code

[github-actions]

HTTP Performance Benchmark

Framework	Runtime	Average	Ping	Query	Body
hono (origin/main)	bun	35,949.50	49,464.55	32,025.50	26,358.44
hono (current)	bun	35,986.48	51,176.80	31,402.10	25,380.53
Change		+0.10%	+3.46%	-1.95%	-3.71%

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.01%. Comparing base (c574cf1) to head (22359f9).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5029   +/-   ##
=======================================
  Coverage   79.01%   79.01%           
=======================================
  Files         154      154           
  Lines       10578    10578           
  Branches     2215     2215           
=======================================
  Hits         8358     8358           
  Misses       2220     2220           

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