The CLEAR HINT syntax is used to clear hint settings for current connection.
ClearHint ::=
  'CLEAR' ('SHARDING' | 'READWRITE_SPLITTING')? 'HINT' 
SHARDING/READWRITE_SPLITTING is not specified, the default is clear all hint settings.CLEAR SHARDING HINT;
CLEAR READWRITE_SPLITTING HINT;
CLEAR HINT;
CLEAR, SHARDING, READWRITE_SPLITTING, HINT
