clear deal message when deal accepted

[dirkmc]

When a deal has been accepted we should clear the deal message.
Otherwise it will still say something like "Provider state: StorageDealVerifyData"

[codecov-io]

Codecov Report

Merging #461 (48b3f45) into master (f24d38e) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #461      +/-   ##
==========================================
+ Coverage   65.50%   65.51%   +0.02%     
==========================================
  Files          46       46              
  Lines        3197     3198       +1     
==========================================
+ Hits         2094     2095       +1     
  Misses        877      877              
  Partials      226      226              

Impacted Files	Coverage Δ
storagemarket/impl/clientstates/client_fsm.go	82.73% <100.00%> (+0.16%)	⬆️

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