ch4/win: skip symm_heap for MPI_Win_allocate_shared

[hzhou]

Pull Request Description

There is no need to try symmetric heap allocation if there is only one node. The symmetric heap trial can easily fail if the segment size is big. The repeated attempts may take up to seconds before giving up.

Fixes #5962

[skip warnings]

Author Checklist

• [x] Provide Description Particularly focus on why, not what. Reference background, issues, test failures, xfail entries, etc.
• [x] Commits Follow Good Practice Commits are self-contained and do not do two things at once. Commit message is of the form: module: short description Commit message explains what's in the commit.
• [ ] Passes All Tests Whitespace checker. Warnings test. Additional tests via comments.
• [x] Contribution Agreement For non-Argonne authors, check contribution agreement. If necessary, request an explicit comment from your companies PR approval manager.

[hzhou]

test:mpich/ch4/ofi