Remove mipmapping + anisotropic filtering for raster tiles

We added a call to generateMipMap on a hunch in #112 a few years ago, and it has remained in the raster drawing code ever since. Mipmaps only make sense when the texture is scaled down significantly (way below 50% of its original size), as a mean to improve the quality of the texels used to calculate the fragment color. A few weeks ago, we added anisotropic filtering to improve the quality.

We never added mipmapping for raster tiles in Native, and I don't think we need to, given that we almost always draw the textures in a size that isn't smaller than half the original dimensions. Since we don't mipmap raster tiles, we also don't need anisotropic filtering.

We should remove the call to generateMipMap and consequently remove anisotropic filtering for raster tiles. This should achieve the near identical visual quality while reducing memory usage and making the code less complex.

https://github.com/mapbox/mapbox-gl-native/issues/8688

Locate the raster drawing code and the existing generateMipMap call, then trace where anisotropic filtering is enabled for raster tiles. Remove both raster-tile settings and verify raster rendering remains visually equivalent while texture setup no longer includes them.