make: Remove unused install-geth target

[Inphi]

A locally installed geth has not been required to run a local devnet or for op-e2e for some time now.
Geth is still used in docker environments, but the user shouldn't be forced to install it locally.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 42.68%. Comparing base (9109958) to head (0da437a).
Report is 3 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #13130      +/-   ##
===========================================
- Coverage    44.46%   42.68%   -1.79%     
===========================================
  Files          798      742      -56     
  Lines        71682    67017    -4665     
===========================================
- Hits         31876    28605    -3271     
+ Misses       37219    36002    -1217     
+ Partials      2587     2410     -177     

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

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see 68 files with indirect coverage changes

[mslipper]

thank god this make target is so annoying