Remove dead URLs from README.md

Author: bikerspade

README.md

@@ -37,10 +37,3 @@ for each supported operating system:
   - [macOS](https://github.com/Screwtapello/higan/releases/download/nightly/higan-macos.zip)
   - [Ubuntu Linux](https://github.com/Screwtapello/higan/releases/download/nightly/higan-ubuntu.zip)
   - [FreeBSD](https://api.cirrus-ci.com/v1/artifact/github/higan-emu/higan/freebsd-x86_64-binaries/higan-nightly/higan-nightly.zip)
-
-Preview
--------
-
-![higan user interface](https://byuu.org/images/higan/higan.png)
-![higan running Bahamut Lagoon (SNES)](https://byuu.org/images/higan/byuu-snes.png)
-![higan running Golden Sun (GBA)](https://byuu.org/images/higan/core-gba.png)