The published download of S4S has a dependency on the Sitecore WFFM (Web Form for Marketers) module. If you are not using WFFM you can open the core zip file and drill down to the following node:
- Sitecore For Salesforce - Core-1.5.13245.1.zip\items\master\sitecore\system\Modules
In this node please delete Web Form for Marketers. This will prevent the WFFM related functionality from being installed. If you have already run the install before, you will be prompted to skip/overwrite items that will now exist. That is expected, so just click through the prompts.
If you require the WFFM functionality to be used with S4S you should install this before installing the S4S Core package.