removed minReadySeconds settings from Searcher and Symbols

[loujar]

This change is proposed because:

1. Symbols and Searcher were switched from Deployment Controllers to StatefulSets in PR 242
2. Kubernetes introduced StatefulSet support for the minReadySeconds configuration in release v1.22
3. Sourcegraph docs advertise support for Kubernetes 1.19+, so we shouldn't ship default k8s configurations that are unsupported in 1.19

Alternative solutions could involve making minReadySeconds a configurable, optional helm value for these STSs, or possibly reverting these two services back to Deployments if we absolutely want to enforce this setting. The impact of removing this setting should be minimal, and we already ship other StatefulSets that do not define minReadySeconds setting.

Checklist

• Follow the manual testing process
• Update changelog

Test plan

1. helm lint charts/sourcegraph/.
2. helm template charts/sourcegraph/ | grep -i "minReadySeconds" -B 2
3. Deployed in GKE reference sandbox to confirm

[scjohns]

lgtm -- just add a test plan so all the checks pass