Delete old duckdb index files

plain_text/train/index.duckdb

@@ -1,3 +0,0 @@
-version https://git-lfs.github.com/spec/v1
-oid sha256:abf69fe7f46295d378a9465277f242fa2e98842032281df764b1145aa7b0f543
-size 69742592

plain_text/validation/index.duckdb

@@ -1,3 +0,0 @@
-version https://git-lfs.github.com/spec/v1
-oid sha256:0b8be62881eeefae6fa0f5d1e44d3b9bbbae7e76358e5e21d531a8581cff6dbf
-size 9449472