Reduce CommandBus

[dmdashenkov]

Previously, the CommandBus checked each command by attempting to route it with the default routing strategy — by the first field.

If a client wants to send a command and it not aware of the receiver, this approach can go wrong. For example, if the first field of a command message happens to be a repeated, the validation fails.

At the same time, command's target can override routing (e.g. a Repository) or not require one at all (e.g. AbstractCommandHandler descendants). It is not possible, however, to pass this information to the CommandBus level.

In this PR we remove this validation step.

After this change, if a command routing fails, we will still get an error and a system event. However, not the users will have more flexibility when defining command messages.

[codecov]

Codecov Report

Merging #1245 into master will increase coverage by 0.02%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master    #1245      +/-   ##
============================================
+ Coverage     91.14%   91.16%   +0.02%     
- Complexity     4807     4809       +2     
============================================
  Files           631      631              
  Lines         15080    15069      -11     
  Branches        848      846       -2     
============================================
- Hits          13744    13738       -6     
+ Misses         1071     1068       -3     
+ Partials        265      263       -2     

[dmdashenkov]

@armiol, PTAL.

[armiol]

@dmdashenkov LGTM, but please make sure you don't submit the same version as @dmitrykuzmin in #1246.