[Exporter.Prometheus] remove redundant if in WriteUnicodeNoEscape

[SimonCropp]

Fixes #
Design discussion issue #

Changes

0x07FF is 2047
0xFFFF is 65535

Since there is ordinal <= 0x07FF check before the ordinal <= 0xFFFF then the ordinal <= 0xFFFF confition is always true

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)
• Unit tests added/updated
• Appropriate CHANGELOG.md files updated for non-trivial changes
• Changes in public API reviewed (if applicable)

[Kielek]

Technically, the change is correct. Maybe it is worth to add some comment about boundaries?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.40%. Comparing base (275a446) to head (935cb4e).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6077   +/-   ##
=======================================
  Coverage   86.39%   86.40%           
=======================================
  Files         257      257           
  Lines       11650    11649    -1     
=======================================
  Hits        10065    10065           
+ Misses       1585     1584    -1     

Files with missing lines	Coverage Δ
...heus.HttpListener/Internal/PrometheusSerializer.cs	87.64% <ø> (+0.48%)	⬆️