gl: rely on QOpenGLExtensions::SRGBFrameBuffer in caps

do not reimplement the same logic that is already there in
qopenglfunctions.cpp

src/rhi/qrhigles2.cpp

@@ -180,10 +180,6 @@ QT_BEGIN_NAMESPACE
 #define GL_FRAMEBUFFER_SRGB 0x8DB9
 #endif
 
-#ifndef GL_FRAMEBUFFER_SRGB_CAPABLE
-#define GL_FRAMEBUFFER_SRGB_CAPABLE 0x8DBA
-#endif
-
 static QSurfaceFormat qrhigles2_effectiveFormat()
 {
     QSurfaceFormat fmt = QSurfaceFormat::defaultFormat();
@@ -314,13 +310,7 @@ bool QRhiGles2::create(QRhi::Flags flags)
     caps.r8Format = f->hasOpenGLFeature(QOpenGLFunctions::TextureRGFormats);
     caps.r16Format = f->hasOpenGLExtension(QOpenGLExtensions::Sized16Formats);
 
-    caps.srgbCapableDefaultFramebuffer = false;
-    if (ctx->hasExtension(QByteArrayLiteral("GL_ARB_framebuffer_sRGB"))) {
-        GLint srgbCapable = 0;
-        f->glGetIntegerv(GL_FRAMEBUFFER_SRGB_CAPABLE, &srgbCapable);
-        if (srgbCapable)
-            caps.srgbCapableDefaultFramebuffer = true;
-    }
+    caps.srgbCapableDefaultFramebuffer = f->hasOpenGLExtension(QOpenGLExtensions::SRGBFrameBuffer);
 
     nativeHandlesStruct.context = ctx;