Removed un-needed features overrides from imagex_search_db.info

## Ready State: Yes

#### Summary

This removes un-needed features overrides from imagex_search_db.info to fix conflicts with overriding project specific features.

#### More Detail

In developing a sitewide search feature for SevOne I was constantly hitting conflicts with the imagex_search_db feature as the sevone feature was exporting `features[features_override_items][] = search_api_index.default_node_index` which imagex_search_db already exported.
We've had similar with features_override previously with other components (can't have more than 1 override of the same config) but on further inspection I noticed imagex_search_db was exporting search_api_index.default_node_index overrides to the .info file (causing the conflict) but not actually using them to override anything.

The imagex_search_db features provides a database server & the only override it requires is to set the node index exported by imagex_search to use the new server.

## Requirements & Dependencies

None

## Deployment Instructions

* Merge code.
* Enable module `imagex_search` & `imagex_search_db`
* Revert the features with `drush fr -y imagex_search imagex_search_db`
* Clear caches with `drush cache-clear all`

## Usage/Test Instructions

* Go to /admin/config/search/search_api & then override some settings in the default_node_index & save
* Go to /admin/structure/features/create & create a feature with those the default_node_index overrides
* Ensure that the new feature & imagex_search_db do not conflict

It maybe be useful to test this with a new installation too with the new project specific overrides enable by default