Fix flaky FileInputStreamTest test.

This file seems to have suffered a bad merge of libcore commit
57afdfdc64eee6693ad7055f3097f30ecce08d82 where on top of the
new code of that CL, some of the (flaky) old code from before
that CL was kept.

This CL fixes that by again deleting the undead (duplicate
and flaky) code that was previously deleted/replaced in the
above libcore commit.

Test: cts-tradefed run cts -a arm64-v8a -m CtsLibcoreTestCases \
Bug: 37238094

Change-Id: I8fccc5d4c51be4b813e53288361f158c7789b9e6
1 file changed