Removes Bank::replace_program_account()

[brooksprumo]

Problem

Bank::replace_program_account() is dead code.

OLD:

When replacing a program via Bank::replace_program_account(), it incorrectly updates the accounts data size.

The fn basically overwrites the old account with the new account. Initially both accounts exist, and afterwards only the new account exists (just now at the old address). So the change in accounts data size is the removal of the old account.

Summary of Changes

Remove it.

[brooksprumo]

@buffalojoec - requesting your review because git blame tells me you're the (potential) author.
@igor56D - requesting your review as someone looking into the accounts data size stuff.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.5%. Comparing base (7fa607c) to head (029fef6).
⚠️ Report is 13 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##           master    #9396     +/-   ##
=========================================
- Coverage    82.5%    82.5%   -0.1%     
=========================================
  Files         895      895             
  Lines      322472   322425     -47     
=========================================
- Hits       266223   266163     -60     
- Misses      56249    56262     +13     

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[buffalojoec]

Yeah, this looks correct to me!

I'm pretty sure we can actually axe this code. I was talking to @Lichtso yesterday and he said this is no longer a safe operation for Loader v2 programs due to the global program cache architecture.

EDIT: I guess I can approve if we plan to keep it, otherwise we can just cut it here.

[Lichtso]

The function is dead_code from two years ago, just delete it.