Remove nanoserver:sac2016 (EOL)

See https://hub.docker.com/r/microsoft/nanoserver:

> The Windows Server 2016-based Nano Server container base image was a Semi-Annual Channel (SAC) release and received its final update on October 23rd, 2018.

Author: tianon

.appveyor.yml

@@ -5,12 +5,8 @@ environment:
   matrix:
     - version: 1.12
       variant: windowsservercore-ltsc2016
-    - version: 1.12
-      variant: nanoserver-sac2016
     - version: 1.11
       variant: windowsservercore-ltsc2016
-    - version: 1.11
-      variant: nanoserver-sac2016
 
 install:
   - ps: |

1.11/windows/nanoserver-sac2016/Dockerfile

@@ -74,7 +74,7 @@ for version in "${versions[@]}"; do
 	for v in \
 		stretch alpine{3.9,3.8} \
 		windows/windowsservercore-{ltsc2016,1803,1809} \
-		windows/nanoserver-{sac2016,1803,1809} \
+		windows/nanoserver-{1803,1809} \
 	; do
 		dir="$version/$v"
 

1.12/windows/nanoserver-sac2016/Dockerfile

@@ -106,7 +106,7 @@ for version in "${versions[@]}"; do
 	done
 
 	for winVariant in \
-		nanoserver-{sac2016,1803,1809} \
+		nanoserver-{1803,1809} \
 		windowsservercore-{ltsc2016,1803,1809} \
 	; do
 		if [ -d "$version/windows/$winVariant" ]; then