Revert "Run docker as the current user (#1630)"

This reverts commit 3539eff.

Makefile

@@ -28,18 +28,12 @@ ifneq ($(SKIP_DOCKER),true)
         $(shell ! docker -v 2>&1 | grep podman >/dev/null ; echo $$?)
     ifeq "$(DOCKER_IS_PODMAN)" "1"
         DOCKER_VOL_SUFFIX = :z
-    else
-        # Real Docker requires this flag so that the files it creates
-        # are owned by the current user instead of root. Podman does
-        # that by default so this flag isn't necessary.
-        DOCKER_USER_ARG := --user $(shell id -u)
     endif
 
     DOCKER_CMD = \
         docker run --rm \
             -v ${PWD}/$@.workdir:/build${DOCKER_VOL_SUFFIX} \
             -w /build \
-            $(DOCKER_USER_ARG) \
             ${DOCKER_IMG} \
             /bin/sh -c
     DOCKER_QUOTE := "