Remove recipient data on resend

[chris-j-h]

This PR fixes a bug when the sender of a payload receives a resend request.

The sender must prune the payload data before resending (i.e. remove the list of recipient keys and only keep the recipient box for the key requesting the resend).

Fixes #770

[codecov-io]

Codecov Report

Merging #766 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##             master     #766      +/-   ##
============================================
+ Coverage     99.45%   99.45%   +<.01%     
  Complexity     1901     1901              
============================================
  Files           287      287              
  Lines          5652     5655       +3     
  Branches        281      281              
============================================
+ Hits           5621     5624       +3     
  Misses            5        5              
  Partials         26       26

Impacted Files	Coverage Δ	Complexity Δ
...um/tessera/transaction/TransactionManagerImpl.java	100% <100%> (ø)	35 <0> (ø)	⬇️

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