Code simplification in plugin tests.

Somehow slipped through ages ago.

src/MagnumPlugins/MagnumFont/Test/MagnumFontGLTest.cpp

@@ -33,8 +33,7 @@
 
 namespace Magnum { namespace Text { namespace Test {
 
-class MagnumFontGLTest: public OpenGLTester {
+struct MagnumFontGLTest: OpenGLTester {
-    public:
     explicit MagnumFontGLTest();
 
     void properties();

src/MagnumPlugins/MagnumFontConverter/Test/MagnumFontConverterGLTest.cpp

@@ -42,8 +42,7 @@
 
 namespace Magnum { namespace Text { namespace Test {
 
-class MagnumFontConverterGLTest: public OpenGLTester {
+struct MagnumFontConverterGLTest: OpenGLTester {
-    public:
     explicit MagnumFontConverterGLTest();
 
     void exportFont();

src/MagnumPlugins/ObjImporter/Test/Test.cpp

@@ -36,8 +36,7 @@
 
 namespace Magnum { namespace Trade { namespace Test {
 
-class ObjImporterTest: public TestSuite::Tester {
+struct ObjImporterTest: TestSuite::Tester {
-    public:
     explicit ObjImporterTest();
 
     void pointMesh();

src/MagnumPlugins/TgaImageConverter/Test/TgaImageConverterTest.cpp

@@ -38,8 +38,7 @@
 
 namespace Magnum { namespace Trade { namespace Test {
 
-class TgaImageConverterTest: public TestSuite::Tester {
+struct TgaImageConverterTest: TestSuite::Tester {
-    public:
     explicit TgaImageConverterTest();
 
     void wrongFormat();

src/MagnumPlugins/TgaImporter/Test/TgaImporterTest.cpp

@@ -37,9 +37,8 @@
 
 namespace Magnum { namespace Trade { namespace Test {
 
-class TgaImporterTest: public TestSuite::Tester {
+struct TgaImporterTest: TestSuite::Tester {
-    public:
+    explicit TgaImporterTest();
-        TgaImporterTest();
 
     void openNonexistent();
     void openShort();

src/MagnumPlugins/WavAudioImporter/Test/WavImporterTest.cpp

@@ -37,8 +37,7 @@
 
 namespace Magnum { namespace Audio { namespace Test {
 
-class WavImporterTest: public TestSuite::Tester {
+struct WavImporterTest: TestSuite::Tester {
-    public:
     explicit WavImporterTest();
 
     void wrongSize();