There should be a way to "unconfigure" the use of of a file based cache for storage sources.  In the longer term, we may have a different layer of the system (block_cache?) handle caching of blocks in files or fragments of files.  In the shorter term, we need our microbenchmarks to run without caching.

Note that loadable extensions have a different way of doing configuration than the rest of WT, typically any options need to be specified when the .so/.dll is loaded into memory.