cmd: Delete temporary env variable LP_IS_ORCH_TESTER

[leszko]

What does this pull request do? Explain your changes. (required)
Orchtester does not use a separate Broadcaster anymore, so the LP_IS_ORCH_TESTER variable is not needed.

Specific updates (required)

• Cleanup

How did you test each of these updates (required)

N/A

Does this pull request close any open issues?
fix livepeer/stream-tester#160

Checklist:

• Read the contribution guide
• make runs successfully
• All tests in ./test.sh pass
• README and other documentation updated
• Pending changelog updated

[codecov]

Codecov Report

Merging #2462 (45e6a64) into master (530051b) will increase coverage by 0.01571%.
The diff coverage is 18.18182%.

@@                 Coverage Diff                 @@
##              master       #2462         +/-   ##
===================================================
+ Coverage   54.86667%   54.88238%   +0.01570%     
===================================================
  Files             94          94                 
  Lines          19726       19724          -2     
===================================================
+ Hits           10823       10825          +2     
+ Misses          8306        8301          -5     
- Partials         597         598          +1     

Impacted Files	Coverage Δ
cmd/livepeer/livepeer.go	50.29940% <ø> (+3.37202%)	⬆️
cmd/livepeer_cli/livepeer_cli.go	0.00000% <0.00000%> (ø)
cmd/livepeer_cli/wizard_transcoder.go	0.00000% <0.00000%> (ø)
server/handlers.go	53.51598% <25.00000%> (-0.10456%)	⬇️
server/webserver.go	95.91837% <100.00000%> (+0.04207%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 71c9654...45e6a64. Read the comment docs.

[victorges]

LGTM