chore: clean up ioutil deprecated methods.

[liangyuanpeng]

1. Does this PR affect any open issues?(Y/N) and add issue references (e.g. "fix #123", "re #123".):

• N
• Y

2. What is the scope of this PR (e.g. component or file name):

3. Provide a description of the PR(e.g. more details, effects, motivations or doc link):

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Other

4. Are there any breaking changes?(Y/N) and describe the breaking changes(e.g. more details, motivations or doc link):

• N
• Y

5. Are there test cases for these changes?(Y/N) select and add more details, references or doc links:

• Unit test
• Integration test
• Benchmark (add benchmark stats below)
• Manual test (add detailed scripts or steps below)
• Other

[coveralls]

Pull Request Test Coverage Report for Build 10519641150

Details

• 1 of 4 (25.0%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 67.785%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pkg/cmds/kcl-openapi.go	0	1	0.0%
pkg/kube_resource/generator/assets/static/gen.go	0	1	0.0%
pkg/swagger/generator/shared.go	1	2	50.0%

Totals
Change from base Build 10466847218:	0.0%
Covered Lines:	2304
Relevant Lines:	3399

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💛 - Coveralls