Update Dockerfile to use piwheels for armv7 (#5709)

docker/build.py

@@ -143,25 +143,15 @@ def main():
         imgs = [f"{params.build_to}:{tag}" for tag in tags_to_push]
         imgs += [f"ghcr.io/{params.build_to}:{tag}" for tag in tags_to_push]
 
-        build_args = [
-            "--build-arg",
-            f"BASEIMGTYPE={params.baseimgtype}",
-            "--build-arg",
-            f"BUILD_VERSION={args.tag}",
-        ]
-
-        if args.arch == ARCH_ARMV7:
-            build_args += [
-                "--build-arg",
-                "PIP_EXTRA_INDEX_URL=https://www.piwheels.org/simple",
-            ]
-
         # 3. build
         cmd = [
             "docker",
             "buildx",
             "build",
-            *build_args,
+            "--build-arg",
+            f"BASEIMGTYPE={params.baseimgtype}",
+            "--build-arg",
+            f"BUILD_VERSION={args.tag}",
             "--cache-from",
             f"type=registry,ref={cache_img}",
             "--file",