Remove "(experimental)" from 3.14+ Windows installer

[itamaro]

Bug report

Bug description:

Currently, the Windows MSI includes the option to "download free-threaded binaries (experimental)".
Since PEP-779 was accepted for the 3.14 release, the "(experimental)" designation should be removed from that option.

CPython versions tested on:

3.14, CPython main branch

Operating systems tested on:

Windows

Linked PRs

• gh-137964: Remove the "experimental" designation from the Windows installer #137965
• [3.14] gh-137964: Remove the "experimental" designation from the Windows installer (GH-137965) #137971

[terryjreedy]

Agreed. PEP 703: Phase I - explicitly experimental. Phase II - officially supported but still optional.
PEP 779: Criteria for Phase II and acceptance that satisfied. "With these criteria satisfied, we believe Python 3.14 is the right time frame for phase II of PEP 703."