DefaultICUTokenizerConfig should use the default ICU behavior for the Khmer script

Recent versions of ICU have their own implementation for the tokenization of the Khmer script. Lucene should not be overriding ICU's behavior any more.

I haven't tried the patch out, but the patch should look something like the following:

$ diff DefaultICUTokenizerConfig.java.orig DefaultICUTokenizerConfig.java
67,68d66
< private static final BreakIterator thaiBreakIterator =
< BreakIterator.getWordInstance(new ULocale("th_TH"));
71,72d68
< private static final BreakIterator khmerBreakIterator =
< readBreakIterator("Khmer.brk");
87d82
< case UScript.THAI: return (BreakIterator)thaiBreakIterator.clone();
89d83
< case UScript.KHMER: return (BreakIterator)khmerBreakIterator.clone();

and the Khmer.* files should be removed. ICU already does script specific tokenization these days. So the Thai one should not be needed either since ICU 50.