RFR: JDK-8258469: Cleanup remaining safefetch test coding

[Thomas Stuefe]

JDK-8257828 fixed SafeFetch for non-java-thread situations on all platforms. It also introduced gtests.
JDK-8185734 fixed the problem that gtests were running without SEH catcher on Windows, preventing us from testing Windows x86 at least.

Since these are fixed, we can remove the related test coding in stubRoutines.cpp.

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Commit messages:
 - Initial

Changes: https://git.openjdk.java.net/jdk/pull/1799/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1799&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8258469
  Stats: 70 lines in 4 files changed: 8 ins; 55 del; 7 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1799.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1799/head:pull/1799

PR: https://git.openjdk.java.net/jdk/pull/1799