Revert "Fix a CharsetEncoder bug."

This reverts commit 653203d1e85f9eca7467ecab60c6000f415aae5d.

Revert "Fix an ASCIICharsetEncoderTest testcase."

This reverts commit fdd61c877cdd981789c976c2418aec0285af7233.

These patches are breaking the tests.api.java.nio.charset.* tests,
back them out. We can't change the underflow conditions without
breaking assumptions in the standard test packages.

Change-Id: I519e21cfef764b7b00fd37d22dc7509f902d3250