RFR: 8304917: Remove unused function declarations in check_classname.h

[Thiago Henrique Hüpner]

Both functions "VerifyClassname" and "VerifyFixClassname" are not used. The functions that are used in the Class.c are "verifyClassname" and "verifyFixClassname", which are declared in the "check_classname.h" header

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Commit messages:
 - Fix copyright
 - Remove unused function declarations

Changes: https://git.openjdk.org/jdk/pull/13077/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13077&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8304917
  Stats: 5 lines in 1 file changed: 0 ins; 4 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/13077.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13077/head:pull/13077

PR: https://git.openjdk.org/jdk/pull/13077