RFR: JDK-8271149: remove unreferenced functions from EncodingSupport_md.c

[Matthias Baesken]

Please review this small change.
I was running into those 2 warnings in EncodingSupport_md.c
function "utfTerminate" was declared but never referenced
function "platformToUtf8" was declared but never referenced

Probably those 2 functions can and should be removed.

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Commit messages:
 - JDK-8271149

Changes: https://git.openjdk.java.net/jdk/pull/4875/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4875&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8271149
  Stats: 27 lines in 1 file changed: 0 ins; 26 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4875.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4875/head:pull/4875

PR: https://git.openjdk.java.net/jdk/pull/4875