RFR: 7903158: jextract crashes due to name clash with pointer to function typedefs

[Athijegannathan Sundararajan]

suffixing $ like it is done already for exception variable in the same source file. Piggybacking to remove unused jtreg header is another test

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Commit messages:
 - 7903158: jextract crashes due to name clash with pointer to function typedefs

Changes: https://git.openjdk.java.net/jextract/pull/21/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jextract&pr=21&range=00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7903158
  Stats: 57 lines in 4 files changed: 45 ins; 8 del; 4 mod
  Patch: https://git.openjdk.java.net/jextract/pull/21.diff
  Fetch: git fetch https://git.openjdk.java.net/jextract pull/21/head:pull/21

PR: https://git.openjdk.java.net/jextract/pull/21