Remove setup service account key information

[nairabhishek73]

From: Set up the service account key
To: If your spreadsheet is viewable by anyone with its link, no further action is needed. If not, give your Service account access to your spreadsheet.

[nairabhishek73]

1. Remove eveything starting from "If your spreadsheet is viewable by anyone with its link, no further action is needed. If not, give your Service account access to your spreadsheet." till If your spreadsheet is viewable by anyone with its link, no further action is needed. If not, give your Service account access to your spreadsheet.

2. REPLACE "Fill in the required credentials." with "Fill in the required credentials. (Refer to OSS credential instructions here: https://docs.airbyte.com/integrations/sources/)