Remove EOL Windows 1803-based (SAC) images

See https://docs.microsoft.com/en-us/virtualization/windowscontainers/deploy-containers/base-image-lifecycle (EOL 11/12/2019)

Makefile

@@ -13,7 +13,6 @@ $(C_TARGETS): hello.c
 	$(STRIP) -R .comment -s '$@'
 	@if [ '$(TARGET_ARCH)' = 'amd64' ]; then \
 		for winVariant in \
-			nanoserver-1803 \
 			nanoserver-1809 \
 		; do \
 			mkdir -p "$(@D)/$$winVariant"; \

amd64/hello-world/nanoserver-1803/Dockerfile

@@ -1,3 +0,0 @@
-FROM mcr.microsoft.com/windows/nanoserver:1803
-COPY hello.txt C:
-CMD ["cmd", "/C", "type C:\\hello.txt"]

amd64/hello-world/nanoserver-1803/hello.txt

@@ -1,22 +0,0 @@
-
-Hello from Docker!
-This message shows that your installation appears to be working correctly.
-
-To generate this message, Docker took the following steps:
- 1. The Docker client contacted the Docker daemon.
- 2. The Docker daemon pulled the "hello-world" image from the Docker Hub.
-    (windows-amd64, nanoserver-1803)
- 3. The Docker daemon created a new container from that image which runs the
-    executable that produces the output you are currently reading.
- 4. The Docker daemon streamed that output to the Docker client, which sent it
-    to your terminal.
-
-To try something more ambitious, you can run a Windows Server container with:
- PS C:\> docker run -it mcr.microsoft.com/windows/servercore powershell
-
-Share images, automate workflows, and more with a free Docker ID:
- https://hub.docker.com/
-
-For more examples and ideas, visit:
- https://docs.docker.com/get-started/
-

generate-stackbrew-library.sh

@@ -62,7 +62,7 @@ for arch in "${arches[@]}"; do
 	EOE
 done
 
-for winVariant in nanoserver-{1803,1809}; do
+for winVariant in nanoserver-1809; do
 	winArches=( *"/$image/$winVariant/hello.txt" )
 	winArches=( "${winArches[@]%"/$image/$winVariant/hello.txt"}" )