Remove unnecessary checks for UnsupportedEncodingException in the client

Many methods in the client need handling of UnsupportedEncodingException, typically because they call String methods that take the name of the encoding as argument. Most of these methods have overloads that take a Charset instead of a String to describe the encoding, and those methods don't throw UnsupportedEncodingException as the encoding is known to be supported once we have a Charset instance for it. We should use the methods that take a Charset and simplify the exception handling.