Proposal: Use SanitizedMessage when possible in svm/account_loader.rs

[LucasSte]

Problem

In svm/src/account_loader.rs SanitizedTransaction is passed between functions in many cases, when just a SanitizedMessage can work without any loss.

Summary of Changes

I swapped SanitizedTransaction for SanitizedMessage in the pertinent locations. One item to be cautious in the review is that I removed one if-condition (see line 131 in account_loader.rs) marked as unused, because the message was previously sanitized, so that the check would never evaluate true.

[codecov]

Codecov Report

Attention: Patch coverage is 94.44444% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 81.7%. Comparing base (e8c87e8) to head (a4de72f).
Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##           master   #35390     +/-   ##
=========================================
- Coverage    81.8%    81.7%   -0.1%     
=========================================
  Files         834      834             
  Lines      224815   224806      -9     
=========================================
- Hits       183919   183874     -45     
- Misses      40896    40932     +36     

[dmakarov]

LGTM