Revert "[BUILD] Always run SQL tests in master build."

This reverts commit 147b6be3b6.

dev/run-tests

@@ -82,9 +82,6 @@ export SBT_MAVEN_PROFILES_ARGS="$SBT_MAVEN_PROFILES_ARGS -Pkinesis-asl"
 if [ -n "$AMPLAB_JENKINS" ]; then
   git fetch origin master:master
 
-  # AMP_JENKINS_PRB indicates if the current build is a pull request build.
-  if [ -n "$AMP_JENKINS_PRB" ]; then
-    # It is a pull request build.
   sql_diffs=$(
     git diff --name-only master \
     | grep -e "^sql/" -e "^bin/spark-sql" -e "^sbin/start-thriftserver.sh"
@@ -104,10 +101,6 @@ if [ -n "$AMPLAB_JENKINS" ]; then
       _SQL_TESTS_ONLY=true
     fi
   fi
-  else
-    # It is a regular build. We should run SQL tests.
-    _RUN_SQL_TESTS=true
-  fi
 fi
 
 set -o pipefail

dev/run-tests-jenkins

@@ -185,8 +185,6 @@ done
 
 # run tests
 {
-  # Marks this build is a pull request build.
-  export AMP_JENKINS_PRB=true
   timeout "${TESTS_TIMEOUT}" ./dev/run-tests
   test_result="$?"