Removing vestigial documentation for dry-run env var

[jake-dog]

As best I can tell the environment variable HELM_DIFF_USE_INSECURE_SERVER_SIDE_DRY_RUN referenced in documentation, originally added in #499, is not actually used anywhere in helm-diff or helm. I also did some testing with and without setting this environment variable and I couldn't see a difference in the helm-diff behavior.

If I'm mistaken then great; this environment variable seems like a good feature broadly speaking. If I'm correct however, then implementing this environment variable now could negatively impact users who have grown accustomed to the default behavior.

[yxxhero]

@jake-dog maybe we should find out why that is not working?

[jake-dog]

Based on my review of commit logs, HELM_DIFF_USE_INSECURE_SERVER_SIDE_DRY_RUN was never implemented. If you prefer that the behavior is implemented as documented, I would be happy to do that. My only reservation is that it could negatively impact users who have grown accustomed to the default behavior.

For reference I ran helm diff upgrade under strace for an existing release using a chart that includes the lookup template function.

app	version
helm	v3.17.3
helm-diff	3.11.0

1. Command: HELM_DIFF_USE_INSECURE_SERVER_SIDE_DRY_RUN=true helm diff upgrade my-release .
   Result: ["helm", "template", "my-release", ".", "--namespace", "helmdifftest", "--values", "/tmp/existing-values2247892059", "--validate", "--is-upgrade", "--dry-run=client"]
lookup called? 🔴

2. Command: helm diff upgrade my-release .
   Result: ["helm", "template", "my-release", ".", "--namespace", "helmdifftest", "--values", "/tmp/existing-values3611432982", "--validate", "--is-upgrade", "--dry-run=client"]
lookup called? 🔴

3. Command: HELM_DIFF_USE_INSECURE_SERVER_SIDE_DRY_RUN=true helm diff upgrade my-release --dry-run .
   Result: ["helm", "template", "my-release", ".", "--namespace", "helmdifftest", "--is-upgrade", "--dry-run=client"]
lookup called? 🔴

4. Command: helm diff upgrade my-release --dry-run .
   Result: ["helm", "template", "my-release", ".", "--namespace", "helmdifftest", "--is-upgrade", "--dry-run=client"]
lookup called? 🔴

5. Command: HELM_DIFF_USE_INSECURE_SERVER_SIDE_DRY_RUN=true helm diff upgrade my-release --dry-run=client
   Result: ["helm", "template", "my-release", ".", "--namespace", "helmdifftest", "--is-upgrade", "--dry-run=client"]
lookup called? 🔴

6. Command: helm diff upgrade my-release --dry-run=client .
   Result: ["helm", "template", "my-release", ".", "--namespace", "helmdifftest", "--is-upgrade", "--dry-run=client"]
lookup called? 🔴

7. Command: HELM_DIFF_USE_INSECURE_SERVER_SIDE_DRY_RUN=true helm diff upgrade my-release --dry-run=server .
   Result: ["helm", "template", "my-release", ".", "--namespace", "helmdifftest", "--values", "/tmp/existing-values3036357848", "--validate", "--is-upgrade", "--dry-run=server"]
lookup called? 🟢

8. Command: helm diff upgrade my-release --dry-run=server .
   Result: ["helm", "template", "my-release", ".", "--namespace", "helmdifftest", "--values", "/tmp/existing-values2789378336", "--validate", "--is-upgrade", "--dry-run=server"]
lookup called? 🟢

9. Command: HELM_DIFF_USE_INSECURE_SERVER_SIDE_DRY_RUN=false helm diff upgrade my-release --dry-run=server .
   Result: ["helm", "template", "my-release", ".", "--namespace", "helmdifftest", "--values", "/tmp/existing-values3326242558", "--validate", "--is-upgrade", "--dry-run=server"]
lookup called? 🟢

If HELM_DIFF_USE_INSECURE_SERVER_SIDE_DRY_RUN is implemented as documented, it would mean that the behavior in test cases 8 & 9 would change to match the result of test cases 1 & 2.