fix(miner)!: remove DEAL_WEIGHT_MULTIPLIER and its input to QAP calc

[rvagg]

Ref: filecoin-project/builtin-actors#1573
Ref: filecoin-project/builtin-actors#1574

Test copied across from Rust.

This will have implications for Lotus because of the breaking API change, it'd probably be worth figuring out how much pain that is before merging this.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 50.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 3.54%. Comparing base (6e096a2) to head (d1961e0).

Files with missing lines	Patch %	Lines
builtin/v15/miner/policy.go	50.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #308      +/-   ##
==========================================
+ Coverage    3.53%    3.54%   +0.01%     
==========================================
  Files         592      592              
  Lines      110759   110757       -2     
==========================================
+ Hits         3915     3931      +16     
+ Misses     105311   105293      -18     
  Partials     1533     1533              

Files with missing lines	Coverage Δ
builtin/network.go	33.33% <ø> (ø)
builtin/v15/miner/policy.go	41.17% <50.00%> (+41.17%)	⬆️

... and 1 file with indirect coverage changes

[Stebalien]

Given that this doesn't actually change the power calculus, the breaking change shouldn't be a huge issue (no need to abstract over different versions, we can just change it everywhere).