chore: remove incorrectly named ToSnakeCase func

[tobikris]

The function was supposed to convert to kebab-case, but named ToSnakeCase. It was removed in favor of using the github.com/stoewer/go-strcase package's KebabCase. This package was already suggested in the documentation anyway.

I verified that this change has no unwanted effects with the following test - no changes in the meaningful cases.

package jsonschema

import (
	"regexp"
	"strings"
	"testing"

	"github.com/stretchr/testify/assert"
)

func TestSnakeCase(t *testing.T) {
        // list from https://github.com/stoewer/go-strcase/blob/master/kebab_test.go#L12
        // except test cases which were not producing useful results before
	data := map[string]string{
		"":      "",
		"F":     "f",
		"Foo":   "foo",
		"FooB":  "foo-b",
		"FooID": "foo-id",
		// " FooBar\t":      "foo-bar",
		"HTTPStatusCode": "http-status-code",
		// "ParseURL.DoParse": "parse-url.do-parse",
		// "Convert Space": "convert-space",
		"Convert-dash": "convert-dash",
		// "Skip___MultipleUnderscores": "skip-multiple-underscores",
		// "Skip   MultipleSpaces":      "skip-multiple-spaces",
		// "Skip---MultipleDashes":      "skip-multiple-dashes",
	}

	for camel, snake := range data {
		converted := ToSnakeCase(camel)
		assert.Equal(t, snake, converted)
	}
}

var (
	matchFirstCap = regexp.MustCompile("(.)([A-Z][a-z]+)")
	matchAllCap   = regexp.MustCompile("([a-z0-9])([A-Z])")
)

// ToSnakeCase converts the provided string into snake case using dashes.
// This is useful for Schema IDs and definitions to be coherent with
// common JSON Schema examples.
func ToSnakeCase(str string) string {
	snake := matchFirstCap.ReplaceAllString(str, "${1}-${2}")
	snake = matchAllCap.ReplaceAllString(snake, "${1}-${2}")
	return strings.ToLower(snake)
}