Replaced deprecated io/ioutil package with proper implementations of …

…io/os packages.

As of Go v1.16, the io/ioutil package has been deprecated and replaced with io and os implementations.
https://go.dev/doc/go1.16#ioutil

.schema/openapi/templates/go/api.mustache

@@ -5,7 +5,7 @@ package {{packageName}}
 import (
 	"bytes"
 	"context"
-	"io/ioutil"
+	"io"
 	"net/http"
 	"net/url"
 {{#imports}}	"{{import}}"
@@ -243,7 +243,7 @@ func (a *{{{classname}}}Service) {{nickname}}Execute(r {{#structPrefix}}{{&class
 	}
 {{/required}}
 	if localVarFile != nil {
-		fbs, _ := ioutil.ReadAll(localVarFile)
+		fbs, _ := io.ReadAll(localVarFile)
 		localVarFileBytes = fbs
 		localVarFileName = localVarFile.Name()
 		localVarFile.Close()
@@ -321,9 +321,9 @@ func (a *{{{classname}}}Service) {{nickname}}Execute(r {{#structPrefix}}{{&class
 		return {{#returnType}}localVarReturnValue, {{/returnType}}localVarHTTPResponse, err
 	}
 
-	localVarBody, err := ioutil.ReadAll(localVarHTTPResponse.Body)
+	localVarBody, err := io.ReadAll(localVarHTTPResponse.Body)
 	localVarHTTPResponse.Body.Close()
-	localVarHTTPResponse.Body = ioutil.NopCloser(bytes.NewBuffer(localVarBody))
+	localVarHTTPResponse.Body = io.NopCloser(bytes.NewBuffer(localVarBody))
 	if err != nil {
 		return {{#returnType}}localVarReturnValue, {{/returnType}}localVarHTTPResponse, err
 	}

.schema/openapi/templates/go/signing.mustache

@@ -14,7 +14,6 @@ import (
 	"encoding/pem"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"net/http"
 	"net/textproto"
 	"os"
@@ -178,7 +177,7 @@ func (h *HttpSignatureAuth) loadPrivateKey() (err error) {
 		err = file.Close()
 	}()
 	var priv []byte
-	priv, err = ioutil.ReadAll(file)
+	priv, err = io.ReadAll(file)
 	if err != nil {
 		return err
 	}