Removed AppVeyor automated build

Now as we have GitHub Actions.

Author: adam-sawicki-a

README.md

@@ -10,10 +10,6 @@ Easy to integrate memory allocation library for Direct3D 12.
 
 **Product page:** [D3D12 Memory Allocator on GPUOpen](https://gpuopen.com/gaming-product/d3d12-memory-allocator/)
 
-**Build status:**
-
-Windows: [![Build status](https://ci.appveyor.com/api/projects/status/860i07bxv55ydgvg?svg=true)](https://ci.appveyor.com/project/adam-sawicki-amd/d3d12memoryallocator)
-
 [![Average time to resolve an issue](http://isitmaintained.com/badge/resolution/GPUOpen-LibrariesAndSDKs/D3D12MemoryAllocator.svg)](http://isitmaintained.com/project/GPUOpen-LibrariesAndSDKs/D3D12MemoryAllocator "Average time to resolve an issue")
 
 # Problem