chore(dockerfile): rm redundant platform paramater

Dockerfile

@@ -1,4 +1,4 @@
-FROM --platform=$TARGETPLATFORM uozi/nginx-ui-base:latest
+FROM uozi/nginx-ui-base:latest
 ARG TARGETOS
 ARG TARGETARCH
 ARG TARGETVARIANT

demo.Dockerfile

@@ -1,5 +1,5 @@
 # CGO_ENABLED=1 GOOS=linux CC=x86_64-unknown-linux-gnu-gcc CXX=x86_64-unknown-linux-gnu-g++ GOARCH=amd64 go build -ldflags "-X 'github.com/0xJacky/Nginx-UI/settings.buildTime=$(date +%s)'" -o nginx-ui -v main.go
-FROM --platform=$TARGETPLATFORM uozi/nginx-ui-base:latest
+FROM uozi/nginx-ui-base:latest
 ARG TARGETOS
 ARG TARGETARCH
 ARG TARGETVARIANT