Revert "git reset before checkout in scripts"

This reverts commit 704056e.
This commit was temporary fix for allowing presubmit perf
tests to pass.

perfmetrics/scripts/presubmit_test/pr_perf_test/build.sh

@@ -87,7 +87,6 @@ if [[ "$perfTestStr" == *"$EXECUTE_PERF_TEST_LABEL"* ]];
 then
  # Executing perf tests for master branch
  install_requirements
- git reset --hard
  git checkout master
  # Store results
  touch result.txt
@@ -97,7 +96,6 @@ then
 
  # Executing perf tests for PR branch
  echo checkout PR branch
- git reset --hard
  git checkout pr/$KOKORO_GITHUB_PULL_REQUEST_NUMBER
  echo Mounting gcs bucket from pr branch and execute tests
  execute_perf_test
@@ -111,7 +109,6 @@ fi
 if [[ "$integrationTestsStr" == *"$EXECUTE_INTEGRATION_TEST_LABEL"* ]];
 then
   echo checkout PR branch
-  git reset --hard
   git checkout pr/$KOKORO_GITHUB_PULL_REQUEST_NUMBER
 
   echo "Running e2e tests...."