test: remove unnecessary testing.T arg

Since the MakePluginDir function takes the TestSuite as receiver, we
don't need to additionally pass in a reference to testing.T, since the
test suite already contains one instance, and offers a function to get
it from.

test/loading_test.go

@@ -7,7 +7,7 @@ import (
 func (ts *PackerTestSuite) TestLoadingOrder() {
 	t := ts.T()
 
-	pluginDir, cleanup := ts.MakePluginDir(t, "1.0.9", "1.0.10")
+	pluginDir, cleanup := ts.MakePluginDir("1.0.9", "1.0.10")
 	defer cleanup()
 
 	for _, command := range []string{"build", "validate"} {

test/plugin_test.go

@@ -140,7 +140,9 @@ func currentDir() (string, error) {
 // packer will be able to use that directory for running its functions.
 //
 // Deletion of the directory is the caller's responsibility.
-func (ts *PackerTestSuite) MakePluginDir(t *testing.T, pluginVersions ...string) (pluginTempDir string, cleanup func()) {
+func (ts *PackerTestSuite) MakePluginDir(pluginVersions ...string) (pluginTempDir string, cleanup func()) {
+	t := ts.T()
+
 	var err error
 
 	defer func() {