Minor cleanups and Javadoc fixes for LdapDnsProvider of java.naming

There are some little flaws in LdapDNSProvider and auxilliary classes, mostly in Javadoc.

In detail:
src/java.naming/share/classes/com/sun/jndi/ldap/DefaultLdapDnsProvider.java: Unnecessary import
src/java.naming/share/classes/com/sun/jndi/ldap/LdapDnsProviderService.java: typo
src/java.naming/share/classes/javax/naming/ldap/spi/LdapDnsProvider.java: Whitespace
src/java.naming/share/classes/javax/naming/ldap/spi/LdapDnsProviderResult.java: Spelling of "ldap" -> should be capitalized