[C++][CI] Remove the macOS workaround for deprecated Abseil APIs in google-cloud-cpp

[hiroyuki-sato]

Describe the enhancement requested

#50887 added a workaround for deprecated Abseil APIs in google-cloud-cpp on macOS.
With the new google-cloud-cpp release > 3.8.0, this workaround is no longer needed, so remove it.

Component(s)

C++, Continuous Integration

[hiroyuki-sato]

• Issue: Deprecation warnings with Abseil 20260526.0 cause build failures with -Werror googleapis/google-cloud-cpp#16354 (Closed)
• PR: chore: migrate from deprecated absl types to std equivalents googleapis/google-cloud-cpp#16400 (Merged)

[aryansk]

take

[hiroyuki-sato]

We need a version of google-cloud-cpp newer than 3.8.0, but no newer version has been released yet, by the way.