fix: remove duplicate tolerations keys for metallb chart

[vespian]

What type of PR is this?
Bug

What this PR does/ why we need it:
Duplicate keys cause Flux to fail, see fluxcd/helm-controller#283 Additionally, the node-role.kubernetes.io/master will no longer be removed/lost in case when new tolerations are defined.

Which issue(s) this PR fixes:

• https://jira.d2iq.com/browse/D2IQ-81473

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

Defining custom tolerations for metallb speaker no longer results in removing/forgetting of `node-role.kubernetes.io/master` toleration.

Checklist

• If a chart is changed, the chart version is correctly incremented.
• The commit message explains the changes and why are needed.
• The code builds and passes lint/style checks locally.
• The relevant subset of integration tests pass locally.
• The core changes are covered by tests.
• The documentation is updated where needed.

[tillt]

lgtm