RFR: 8270453: [JVMCI] remove duplicates in vmStructs_jvmci.cpp

[Doug Simon]

Removes some duplicate exports in vmStructs_jvmci.cpp.

I've tested by comparing the output of `java -XX:+UnlockExperimentalVMOptions -XX:+EnableJVMCI -XX:+EagerJVMCI -Djvmci.PrintConfig=true -version` before and after this change.

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Commit messages:
 - remove duplicates exports

Changes: https://git.openjdk.java.net/jdk/pull/4779/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4779&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8270453
  Stats: 7 lines in 1 file changed: 0 ins; 7 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4779.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4779/head:pull/4779

PR: https://git.openjdk.java.net/jdk/pull/4779