remove 'sudo -u $USER' in examples page

In the 'RecordService to Control Column-level Access' section, when we use Impala to select all records from the rs.employees table, the cmd we are using is "sudo -u $USER impala-shell". It is actually redundant. If we want to run impala-shell with the current user, we do not need to change user.
So we need update 'sudo -u $USER impala-shell' to 'impala-shell'