Remove unnecessary # syntax=docker/dockerfile:1 directive from AOT Dockerfiles

BuildKit is the default builder since Docker/Moby 23.0, and imagebuilder
runs moby-engine 25.0.3 on Azure Linux 3.0. The syntax directive is no
longer needed. Removing it avoids pulling a remote image under network
isolation.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: lbussell

eng/dockerfile-templates/sdk/Dockerfile.linux.aot

@@ -26,8 +26,7 @@
             "llvm"
         ]))))
 
-}}# syntax=docker/dockerfile:1
-ARG REPO=mcr.microsoft.com/dotnet/sdk
+}}ARG REPO=mcr.microsoft.com/dotnet/sdk
 FROM {{baseImageTag}}
 
 RUN {{InsertTemplate("../Dockerfile.linux.install-pkgs", [ "pkgs": pkgs ])}}

eng/dockerfile-templates/sdk/Dockerfile.linux.aot-cross

@@ -26,8 +26,7 @@
             "http://archive.ubuntu.com/ubuntu/",
             "http://ports.ubuntu.com/ubuntu-ports/")
 
-}}# syntax=docker/dockerfile:1
-ARG REPO=mcr.microsoft.com/dotnet/sdk
+}}ARG REPO=mcr.microsoft.com/dotnet/sdk
 FROM {{baseImageTag}}
 
 {{if match(OS_VERSION, "jammy"):RUN echo "deb [arch={{targetArchShortName}}] {{ubuntuPortsUrl}} {{OS_VERSION}} main restricted" > {{sourcesListFilePath}} \

src/sdk/10.0/alpine3.23-aot/amd64/Dockerfile

@@ -1,4 +1,3 @@
-# syntax=docker/dockerfile:1
 ARG REPO=mcr.microsoft.com/dotnet/sdk
 FROM $REPO:10.0.201-alpine3.23-amd64
 

src/sdk/10.0/alpine3.23-aot/arm64v8/Dockerfile

@@ -1,4 +1,3 @@
-# syntax=docker/dockerfile:1
 ARG REPO=mcr.microsoft.com/dotnet/sdk
 FROM $REPO:10.0.201-alpine3.23-arm64v8
 

src/sdk/10.0/azurelinux3.0-aot/amd64/Dockerfile

@@ -1,4 +1,3 @@
-# syntax=docker/dockerfile:1
 ARG REPO=mcr.microsoft.com/dotnet/sdk
 FROM $REPO:10.0.201-azurelinux3.0-amd64
 

src/sdk/10.0/azurelinux3.0-aot/arm64v8/Dockerfile

@@ -1,4 +1,3 @@
-# syntax=docker/dockerfile:1
 ARG REPO=mcr.microsoft.com/dotnet/sdk
 FROM $REPO:10.0.201-azurelinux3.0-arm64v8
 

src/sdk/10.0/noble-aot/amd64/Dockerfile

@@ -1,4 +1,3 @@
-# syntax=docker/dockerfile:1
 ARG REPO=mcr.microsoft.com/dotnet/sdk
 FROM $REPO:10.0.201-noble-amd64
 

src/sdk/10.0/noble-aot/arm64v8/Dockerfile

@@ -1,4 +1,3 @@
-# syntax=docker/dockerfile:1
 ARG REPO=mcr.microsoft.com/dotnet/sdk
 FROM $REPO:10.0.201-noble-arm64v8
 

src/sdk/10.0/resolute-aot/amd64/Dockerfile

@@ -1,4 +1,3 @@
-# syntax=docker/dockerfile:1
 ARG REPO=mcr.microsoft.com/dotnet/sdk
 FROM $REPO:10.0.201-resolute-amd64
 

src/sdk/10.0/resolute-aot/arm64v8/Dockerfile

@@ -1,4 +1,3 @@
-# syntax=docker/dockerfile:1
 ARG REPO=mcr.microsoft.com/dotnet/sdk
 FROM $REPO:10.0.201-resolute-arm64v8