[lworld] RFR: 8352727: [lworld] Remove or replace obsolete StressInlineTypeReturnedAsFields flag from tests

[Christian Hagedorn]

[JDK-8301007](https://bugs.openjdk.org/browse/JDK-8301007) renamed `StressInlineTypeReturnedAsFields` to `StressCallingConvention` and added some more stressing possibilities. However, it was forgotten to update the flag in tests in two locations:

### Use in Default Scenario

One default scenario uses `-XX:+StressInlineTypeReturnedAsFields` for Valhalla IR tests. The tests still succeed because we have `-XX:+IgnoreUnrecognizedVMOptions` in place which ignores the now non-existing flag.

I tried to replace `StressInlineTypeReturnedAsFields` with the updated `StressCallingConvention` flag but it turns out that too many IR rules rely on a predictable calling convention such that we could verify that all allocations are removed. With `StressCallingConvention`, we could now randomly enforce allocations because we cannot pass a value object in scalarized form anymore because there is only a non-scalarized calling convention.

I therefore propose to simply drop `StressInlineTypeReturnedAsFields` from the default scenario without replacement. 

Note that we still have stress jobs in place that run with `StressCallingConvention` enabled to exercise different combinations of calling conventions.


### Use in `TestCallingConventionC1.java`
The second use in `TestCallingConventionC1.java` can be replaced by `StressCallingConvention` because we do not have any IR rules that could be affected.

Thanks,
Christian

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Commit messages:
 - 8352727: [lworld] Remove or replace obsolete StressInlineTypeReturnedAsFields flag from tests

Changes: https://git.openjdk.org/valhalla/pull/1412/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1412&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8352727
  Stats: 3 lines in 2 files changed: 0 ins; 1 del; 2 mod
  Patch: https://git.openjdk.org/valhalla/pull/1412.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1412/head:pull/1412

PR: https://git.openjdk.org/valhalla/pull/1412