[foreign-jextract] RFR: 8266414: jextract should not generate NativeScope

[Athijegannathan Sundararajan]

removed NativeScope and adjusted tests

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Commit messages:
 - 8266414: jextract should not generate NativeScope

Changes: https://git.openjdk.java.net/panama-foreign/pull/525/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=525&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8266414
  Stats: 91 lines in 9 files changed: 12 ins; 66 del; 13 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/525.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/525/head:pull/525

PR: https://git.openjdk.java.net/panama-foreign/pull/525