gh-131296: fix clang-cl warning in tracemalloc.c

[vstinner]

Always set MAX_NFRAME to UINT16_MAX.

Avoid the complicated code which emitted a compiler warning.

• Issue: clang-cl issues many warnings when building on Windows #131296

[vstinner]

65535 is already the effective limit:

$ python
Python 3.13.2 (main, Feb  4 2025, 00:00:00) [GCC 14.2.1 20250110 (Red Hat 14.2.1-7)] on linux
Type "help", "copyright", "credits" or "license" for more information.

>>> import tracemalloc; tracemalloc.start(2**16+1)
Traceback (most recent call last):
ValueError: the number of frames must be in range [1; 65535]