DatabaseRecordList: Drop hook to modify searchFields
The TCA configuration searchFields in the ctrl section has been
introduced in TYPO3 4.6.
This configuration allows to set columns. Those columns are
taken into account by the search in the TYPO3 backend.
To enable a smooth transition between TYPO3 4.5 and 4.6, the hook
['getSearchFieldList'] has been introduced as well. It allows
to set the searchFields for the list module's search.
As this transition should be finished now, the hook could be
removed. Extension authors should set the searchFields via
the TCA configuration.