AMDGPU/R600: Don't set fp32-denormals feature for r600

[jvesely]

Summary

This feature was removed in r335942.

[jvesely]

D49934

lib/Target/AMDGPU/AMDGPUSubtarget.cpp

   // if someone tries to enable these?
   if (getGeneration() >= AMDGPUSubtarget::SOUTHERN_ISLANDS) {
     FullFS += "+fp64-fp16-denormals,";
-  } else {
-    FullFS += "-fp32-denormals,";
   }
 
   FullFS += FS;