Remove ENV support from rspec-stackprof

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/179436



Merged-by: Thong Kuah <tkuah@gitlab.com>
Approved-by: Leala Smith <lsmith@gitlab.com>
Approved-by: Hitesh Raghuvanshi <hraghuvanshi@gitlab.com>
Approved-by: Thong Kuah <tkuah@gitlab.com>
Co-authored-by: AMOUSSOU Z. Kenneth <kenneth.amoussou@gmail.com>