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 4e65c1c319.
Signed-off-by: Tibor Vass <tibor@docker.com>
0252ad0adc