What this PR does / why we need it:
remove BaseDataSource's allowEncodingChanges in reference function to avoid double print in getUrl function.
Which issue this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged): fixes
#I3X5AQ:org.postgresql.test.jdbc2.optional.BaseDataSourceTest的testJndi方法失败

Special notes for your reviewer:

1. ((PgConnection) con).getQueryExecutor().getBackendPID() is not true gauss pid, need use select pg_backend_pid() to query it.
   Release note:

test case passed: