GLX: Use glXCreateContextAttribsARB to create versioned context. It makes RenderDoc work without specifying GL version.

src/glcontext_glx.cpp

@@ -164,7 +164,6 @@ namespace bgfx { namespace gl
 			m_context = glXCreateContext(m_display, m_visualInfo, 0, GL_TRUE);
 			BGFX_FATAL(NULL != m_context, Fatal::UnableToInitialize, "Failed to create GL 2.1 context.");
 
-#if BGFX_CONFIG_RENDERER_OPENGL >= 31
 			glXCreateContextAttribsARB = (PFNGLXCREATECONTEXTATTRIBSARBPROC)glXGetProcAddress( (const GLubyte*)"glXCreateContextAttribsARB");
 
 			if (NULL != glXCreateContextAttribsARB)
@@ -188,9 +187,6 @@ namespace bgfx { namespace gl
 					m_context = context;
 				}
 			}
-#else
-			BX_UNUSED(bestConfig);
-#endif // BGFX_CONFIG_RENDERER_OPENGL >= 31
 
 			XUnlockDisplay(m_display);
 		}