Remove ioutil package from Pipecd's dependencies

[khanhtc1202]

What this PR does / why we need it:

Remove ioutil package since the APIs of ioutil are deprecated.

Confirmed ioutil package is completely removed with

╭─ ~/workspace/pipecd/pipe  remove-ioutil !1 ────────────────────── ✔  11:15:54 
╰─ ag --go "ioutil"

Which issue(s) this PR fixes:

Fixes #

Does this PR introduce a user-facing change?:

NONE

[pipecd-bot]

The following files are not gofmt-ed. By commenting /golinter fmt, the formatted one will be appended to this pull request automatically.

pkg/git/commit_test.go

--- pkg/git/commit_test.go.orig
+++ pkg/git/commit_test.go
@@ -28,7 +28,7 @@
 	require.NoError(t, err)
 
 	expected := []Commit{
-		Commit{
+		{
 			Author:          "nghialv",
 			Committer:       "kapetanios-robot",
 			CreatedAt:       1565752022,
@@ -36,7 +36,7 @@
 			AbbreviatedHash: "74e20ed",
 			Message:         "wip",
 		},
-		Commit{
+		{
 			Author:          "Le Van Nghia",
 			Committer:       "kapetanios-robot",
 			CreatedAt:       1565749682,
@@ -59,7 +59,7 @@
 
 This PR was merged by Kapetanios.`,
 		},
-		Commit{
+		{
 			Author:          "nghialv",
 			Committer:       "kapetanios-robot",
 			CreatedAt:       2565752022,

[khanhtc1202]

/golinter fmt

[pipecd-bot]

Code coverage for golang is 31.62%. This pull request decreases coverage by -0.12%.

File	Function	Base	Head	Diff
pkg/app/piped/executor/analysis/metrics_analyzer.go	metricsAnalyzer.analyzeWithPrevious	0.00%	0.00%	+0.00%
pkg/app/piped/executor/analysis/metrics_analyzer.go	metricsAnalyzer.analyzeWithCanaryBaseline	0.00%	0.00%	+0.00%
pkg/app/piped/executor/analysis/metrics_analyzer.go	metricsAnalyzer.analyzeWithCanaryPrimary	0.00%	0.00%	+0.00%
pkg/app/piped/executor/analysis/metrics_analyzer.go	compare	73.68%	78.95%	+5.26%

[pipecd-bot]

Code coverage for golang is 31.62%. This pull request decreases coverage by -0.12%.

File	Function	Base	Head	Diff
pkg/app/piped/executor/analysis/metrics_analyzer.go	metricsAnalyzer.analyzeWithPrevious	0.00%	0.00%	+0.00%
pkg/app/piped/executor/analysis/metrics_analyzer.go	metricsAnalyzer.analyzeWithCanaryBaseline	0.00%	0.00%	+0.00%
pkg/app/piped/executor/analysis/metrics_analyzer.go	metricsAnalyzer.analyzeWithCanaryPrimary	0.00%	0.00%	+0.00%
pkg/app/piped/executor/analysis/metrics_analyzer.go	compare	73.68%	78.95%	+5.26%

[nakabonne]

Nice work. They all seem to be the correct replacements.
/lgtm

[nghialv]

Feel so good!
/approve

[pipecd-bot]

This pull request is APPROVED by nghialv.

Approvers can cancel the approval by writing /approve cancel in a comment. Any additional commits also will change this pull request to be not-approved.