ClearTextureFilters will definetly work, but, it will also disable mipmaps from working, so make sure when loading your textures you use the mipmap load flag.
If you don't want to do that, you could use the copyrect command to copy the entire texture back onto itself, wiping any alpha from the texture.
If you don't want to do that, you could use the copyrect command to copy the entire texture back onto itself, wiping any alpha from the texture.