e2e: do not set a user for raw_exec tasks (#17901)

Cannot set a user for raw_exec tasks, because doing so does not work
with the 0700 root owned client data directory that we setup in the e2e
cluster in accordance with the Nomad hardening guide.

e2e/example/input/env.hcl

@@ -23,7 +23,6 @@ job "env" {
     }
 
     task "task" {
-      user   = "nobody"
       driver = "raw_exec"
 
       config {

e2e/example/input/sleep.hcl

@@ -28,7 +28,6 @@ job "sleep" {
     }
 
     task "task" {
-      user   = "nobody"
       driver = "raw_exec"
 
       config {

e2e/servicediscovery/input/checks_task_restart_main.nomad

@@ -35,7 +35,6 @@ job "checks_task_restart" {
 
     task "python" {
       driver = "raw_exec"
-      user   = "nobody"
       config {
         command = "python3"
         args    = ["-m", "http.server", "${NOMAD_PORT_http}", "--directory", "/tmp"]