api: POST /build: remove version-gate for "pull" (api < v1.16)

The "pull" option was added in API v1.16 (Docker Engine v1.4.0) in commit
054e57a622e6a065c343806e7334920d17a03c5b, which gated the option by API
version.

API v1.23 and older are deprecated, so we can remove the gate.

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

api/server/router/build/build_routes.go

@@ -42,6 +42,7 @@ func newImageBuildOptions(ctx context.Context, r *http.Request) (*types.ImageBui
 		SuppressOutput: httputils.BoolValue(r, "q"),
 		NoCache:        httputils.BoolValue(r, "nocache"),
 		ForceRemove:    httputils.BoolValue(r, "forcerm"),
+		PullParent:     httputils.BoolValue(r, "pull"),
 		MemorySwap:     httputils.Int64ValueOrZero(r, "memswap"),
 		Memory:         httputils.Int64ValueOrZero(r, "memory"),
 		CPUShares:      httputils.Int64ValueOrZero(r, "cpushares"),
@@ -74,9 +75,6 @@ func newImageBuildOptions(ctx context.Context, r *http.Request) (*types.ImageBui
 		options.Remove = httputils.BoolValue(r, "rm")
 	}
 	version := httputils.VersionFromContext(ctx)
-	if httputils.BoolValue(r, "pull") && versions.GreaterThanOrEqualTo(version, "1.16") {
-		options.PullParent = true
-	}
 	if versions.GreaterThanOrEqualTo(version, "1.32") {
 		options.Platform = r.FormValue("platform")
 	}