RFR: 8259486: Remove CautiouslyPreserveExceptionMark

[Coleen Phillimore]

See CR for details.  This is a hopefully simple cleanup.  I didn't try to reason about removing any of these except an obvious call (if you look above the patch in thread.cpp).
Tested with tier1-3.

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Commit messages:
 - Fix clear_pending_exception in fill_in_stack_trace.
 - Remove CautiouslyPreserveException mark.

Changes: https://git.openjdk.java.net/jdk/pull/2007/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2007&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8259486
  Stats: 103 lines in 14 files changed: 8 ins; 58 del; 37 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2007.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2007/head:pull/2007

PR: https://git.openjdk.java.net/jdk/pull/2007