Remove MagickWand-config and Magick-config configuration (#422)
Remove MagickWand-config and Magick-config configuration (#422)

`MagickWand-config` and `Magick-config` depend on `pkg-config` command.
If remove `pkg-config`, `MagickWand-config` and `Magick-config` does not work.

```
$ brew uninstall --ignore-dependencies pkg-config
Uninstalling /usr/local/Cellar/pkg-config/0.29.2... (11 files, 627.2KB)

$ ./MagickWand-config --cflags
./MagickWand-config: line 41: pkg-config: command not found
$ ./Magick-config --cflags
./Magick-config: line 41: pkg-config: command not found
```

And `pkg-config` can take same value of `MagickWand-config`.

```
$ pkg-config --cflags MagickWand
-DMAGICKCORE_HDRI_ENABLE=0 -DMAGICKCORE_QUANTUM_DEPTH=16 -DMAGICKCORE_HDRI_ENABLE=0 -DMAGICKCORE_QUANTUM_DEPTH=16 -I/Users/watson/imagemagick/include/ImageMagick-6
$ ./MagickWand-config --cflags
-DMAGICKCORE_HDRI_ENABLE=0 -DMAGICKCORE_QUANTUM_DEPTH=16 -DMAGICKCORE_HDRI_ENABLE=0 -DMAGICKCORE_QUANTUM_DEPTH=16 -I/Users/watson/imagemagick/include/ImageMagick-6
```

So, we can remove the configuration of MagickWand-config and Magick-config part.
rmagick/rmagick,rmagick/rmagick,rmagick/rmagick