Drop luni's duplicate {Matcher2,Mode,Replace,Split}Test.java.

These files are identical to the ones in a slightly different package in harmony-tests,
except that luni's SplitTest was missing a file header.

To avoid future divergence, this CL drops the copy in luni/.

PatternTest and PatternSyntaxExceptionTest remain in luni
(harmony-tests/ has PatternErrorTest and MatcherTest instead).

Bug: 109727025
Test Treehugger
Test: Ran CtsLibcoreTestCases at a later CL.

Change-Id: I83f59fe5dcceeffe3231d1db1de47758c0d1d92b