Platform: drop another compatibility branch for old Emscripten.

src/Magnum/Platform/EmscriptenApplication.cpp

@@ -341,16 +341,9 @@ bool EmscriptenApplication::tryCreate(const Configuration& configuration, const
         !!(glConfiguration.flags() & GLConfiguration::Flag::PremultipliedAlpha);
     attrs.preserveDrawingBuffer =
         !!(glConfiguration.flags() & GLConfiguration::Flag::PreserveDrawingBuffer);
-    /* powerPreference replaced preferLowPowerToHighPerformance in emscripten
-       version 1.38.26 */
-    #ifdef EM_WEBGL_POWER_PREFERENCE_LOW_POWER
     attrs.powerPreference =
         !!(glConfiguration.flags() & GLConfiguration::Flag::PreferLowPowerToHighPerformance)
         ? EM_WEBGL_POWER_PREFERENCE_LOW_POWER : EM_WEBGL_POWER_PREFERENCE_HIGH_PERFORMANCE;
-    #else
-    attrs.preferLowPowerToHighPerformance =
-        !!(glConfiguration.flags() & GLConfiguration::Flag::PreferLowPowerToHighPerformance);
-    #endif
     attrs.explicitSwapControl =
         !!(glConfiguration.flags() & GLConfiguration::Flag::ExplicitSwapControl);
     attrs.failIfMajorPerformanceCaveat =