batcher: fix state inconsistency

[geoknee]

The new batcher got into a bad state when rolled out to devnet.

1. The batcher started up and behaved normally
2. The sequencer restarted
3. When it came back up, it's safe head went backwards
4. The batcher detected this, and tried to clear out its state and start work from the new safe head
5. It did not clear its state properly, and the consistency caused it to constantly run into 4 over and over.

This PR removes some redundant state which was not being cleared, which should fix the problem.

[codecov]

Codecov Report

Attention: Patch coverage is 4.34783% with 22 lines in your changes missing coverage. Please review.

Project coverage is 42.85%. Comparing base (601af96) to head (2234b92).
Report is 5 commits behind head on develop.

Files with missing lines	Patch %	Lines
op-batcher/batcher/driver.go	0.00%	17 Missing ⚠️
op-batcher/batcher/channel_manager.go	16.66%	5 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #12981      +/-   ##
===========================================
- Coverage    44.55%   42.85%   -1.70%     
===========================================
  Files          799      743      -56     
  Lines        71845    67184    -4661     
===========================================
- Hits         32009    28792    -3217     
+ Misses       37230    35968    -1262     
+ Partials      2606     2424     -182     

Flag	Coverage Δ
cannon-go-tests-32	?
cannon-go-tests-64	?

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

Files with missing lines	Coverage Δ
op-batcher/batcher/channel_manager.go	86.92% <16.66%> (-1.17%)	⬇️
op-batcher/batcher/driver.go	3.84% <0.00%> (+0.01%)	⬆️

... and 62 files with indirect coverage changes