cannon: Clean up program patching

[mbaxter]

Description

This PR does a little bit of clean-up around Cannon patching:

• Remove some TODOs that we no longer need
• Rename patchGo to patchGoGC for clarity, add some comments
• Only allow go gc patching for single-threaded Cannon in the load-elf command

Tests

Manually tested the load-elf changes.

Metadata

Relates to: #11654

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.20%. Comparing base (57f9fbf) to head (273bf9e).
Report is 6 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop   #11944   +/-   ##
========================================
  Coverage    79.20%   79.20%           
========================================
  Files           41       41           
  Lines         3414     3414           
========================================
  Hits          2704     2704           
  Misses         541      541           
  Partials       169      169           

Flag	Coverage Δ
cannon-go-tests	79.20% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
cannon/mipsevm/exec/mips_syscalls.go	93.75% <ø> (ø)
cannon/mipsevm/program/patch.go	83.92% <100.00%> (ø)
cannon/mipsevm/testutil/elf.go	100.00% <100.00%> (ø)

[Inphi]

Might also be worth removing the --patch option altogether and hardcoding stack and go for st-cannon. Unless there's a usecase for loading singlethreaded Go programs via the cannon cli.

[mbaxter]

Might also be worth removing the --patch option altogether

Yeah, good call. Went ahead and cut this out.