Update internal build script (#7957)

Summary:
For internal build.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7957

Test Plan: https://www.internalfb.com/intern/sandcastle/group/nonce/6483925578523975/

Reviewed By: ltamasi

Differential Revision: D26410919

Pulled By: jay-zhuang

fbshipit-source-id: a5f9516c91ea85c384a4208aa73331ecad833d01

tools/regression_test.sh

@@ -158,7 +158,7 @@ function init_arguments {
 
   current_time=$(date +"%F-%H:%M:%S")
   RESULT_PATH=${RESULT_PATH:-"$1/results/$current_time"}
-  COMMIT_ID=`git log | head -n1 | cut -c 8-`
+  COMMIT_ID=`hg id -i`
   SUMMARY_FILE="$RESULT_PATH/SUMMARY.csv"
 
   DB_PATH=${3:-"$1/db"}
@@ -367,16 +367,6 @@ function exit_on_error {
   fi
 }
 
-function checkout_rocksdb {
-  echo "Checking out commit $1 ..."
-
-  git fetch --all
-  exit_on_error $?
-
-  git checkout $1
-  exit_on_error $?
-}
-
 function build_db_bench_and_ldb {
   echo "Building db_bench & ldb ..."