scripts/build/plugins: don't -buildmode=pie without CGO enabled

The `.variables` sets `CGO_ENABLED=1` on arm; https://github.com/docker/cli/blob/b0c41b78d8c80c5f8faa736cf3c74dc31092e443/scripts/build/.variables#L57-L68
And if enabled, it sets `-buildmode=pie`; https://github.com/docker/cli/blob/b0c41b78d8c80c5f8faa736cf3c74dc31092e443/scripts/build/.variables#L79-L88

But that looks to be conflicting with the hard-coded `CGO_ENABLED=0` in
this script.

    > [build-plugins 1/1] RUN --mount=ro --mount=type=cache,target=/root/.cache     xx-go --wrap &&     TARGET=/out ./scripts/build/plugins e2e/cli-plugins/plugins/*:
    0.127 Building static docker-helloworld
    0.127 + CGO_ENABLED=0
    0.127 + GO111MODULE=auto
    0.127 + go build -o /out/plugins-linux-arm/docker-helloworld -tags ' osusergo' -ldflags ' -X "github.com/docker/cli/cli/version.GitCommit=5c123b1" -X "github.com/docker/cli/cli/version.BuildTime=2024-09-02T13:52:17Z" -X "github.com/docker/cli/cli/version.Version=pr-5387" -extldflags -static' -buildmode=pie github.com/docker/cli/cli-plugins/examples/helloworld
    0.135 -buildmode=pie requires external (cgo) linking, but cgo is not enabled

Remove `GO_BUILDMODE` from this script so that we don't try to build
with `-buildmode=pie`.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

scripts/build/plugins

@@ -15,5 +15,5 @@ for p in cli-plugins/examples/* "$@" ; do
     mkdir -p "$(dirname "${TARGET_PLUGIN}")"
 
     echo "Building $GO_LINKMODE $(basename "${TARGET_PLUGIN}")"
-    (set -x ; CGO_ENABLED=0 GO111MODULE=auto go build -o "${TARGET_PLUGIN}" -tags "${GO_BUILDTAGS}" -ldflags "${GO_LDFLAGS}" ${GO_BUILDMODE} "github.com/docker/cli/${p}")
+    (set -x ; CGO_ENABLED=0 GO111MODULE=auto go build -o "${TARGET_PLUGIN}" -tags "${GO_BUILDTAGS}" -ldflags "${GO_LDFLAGS}" "github.com/docker/cli/${p}")
 done