remove deleted option from benchmark.sh

Summary:
Removed max_grandparent_overlap_factor from benchmark.sh since it is not a valid option anymore.
Closes https://github.com/facebook/rocksdb/pull/2015

Differential Revision: D4748229

Pulled By: lgalanis

fbshipit-source-id: c3869ea

tools/benchmark.sh

@@ -86,7 +86,6 @@ const_params="
   \
   --verify_checksum=1 \
   --delete_obsolete_files_period_micros=$((60 * M)) \
-  --max_grandparent_overlap_factor=8 \
   --max_bytes_for_level_multiplier=8 \
   \
   --statistics=0 \