Remove unused README files.

These files were from an obsolete ANGLE integration.

Bug: 843346
Tbr: thakis@chromium.org
Change-Id: I630cf9c5126c979fa28c768f04cafb80dceb2083
Reviewed-on: https://chromium-review.googlesource.com/c/1316594
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Chris Blume <cblume@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605220}

third_party/glslang-angle/README.chromium

-Name: Khronos reference front-end for GLSL and ESSL
-Short Name: glslang
-URL: https://github.com/google/glslang
-Version: unknown
-Security Critical: yes
-License: MIT
-License File: LICENSE
-
-Description:
-An OpenGL and OpenGL ES shader front end and validator.

third_party/spirv-tools-angle/README.chromium

-Name: SPIR-V Tools
-Short Name: SPIRV-Tools
-URL: https://github.com/KhronosGroup/SPIRV-Tools.git
-Version: unknown
-Security Critical: yes
-License: MIT
-License File: LICENSE
-
-Description:
-The SPIR-V Tools project provides an API and commands for processing
-SPIR-V modules.

third_party/vulkan-validation-layers/README.chromium

-Name: Vulkan Ecosystem Components
-Short Name: Vulkan Layers SDK
-Version: unknown
-URL: https://github.com/KhronosGroup/Vulkan-LoaderAndValidationLayers
-SOURCE CODE: git clone https://github.com/KhronosGroup/Vulkan-LoaderAndValidationLayers.git
-Date: 06/07/2016
-Revision: d9da90d92748c37962766868f8b0354637672c2a
-Security Critical: no
-License: Apache 2.0
-License File: LICENSE.txt
-
-Description:
-The Vulkan Ecosystem Components consist of the Vulkan loader and Validation Layers SDK. The layers help
-validate Vulkan programs at runtime for development, and the loader is a utility for loading the Vulkan
-entry points and hooking them into the correct layers. These are essential for developing Vulkan
-applications.
-