dcrd: Remove unused old chainindexer file.
dcrd: Remove unused old chainindexer file.

The chainindexer.go file is completely commented out and has been
replaced by a new indexing infrastructure.  This removes the entire file
since it is no longer required.

jrick/btcd,jrick/dcrd,jcmincke/dcrd,jrick/btcd,jcmincke/dcrd,decred/dcrd,jrick/dcrd,decred/dcrd,jrick/btcd,jcmincke/dcrd