The validation script from #10681 is too pedantic, and does not handle
well situations like:
```
cat <<EOF # or <<-EOF
Whether the leading whitespace is stripped out or not by bash
it should still be considered as valid.
EOF
```
This reverts commit 4e65c1c319afffc325853b88c9aef0c42ec83482.
Signed-off-by: Tibor Vass <tibor@docker.com>
Upstream-commit: 0252ad0adc37a34b88fa908ae74a13b940febdcb
Component: engine
abd71318ca