Removing all but windows builds from Travis

[algojack]

We moved everything but windows to CircleCI, this is just cleaning up.

[codecov-commenter]

Codecov Report

Merging #3154 (c611ba1) into master (729e597) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #3154   +/-   ##
=======================================
  Coverage   43.78%   43.78%           
=======================================
  Files         391      391           
  Lines       86880    86880           
=======================================
  Hits        38038    38038           
+ Misses      42808    42806    -2     
- Partials     6034     6036    +2     

Impacted Files	Coverage Δ
crypto/merkletrie/trie.go	66.42% <0.00%> (-2.19%)	⬇️
crypto/merkletrie/node.go	91.62% <0.00%> (-1.87%)	⬇️
data/abi/abi_type.go	92.03% <0.00%> (-1.00%)	⬇️
network/wsPeer.go	70.93% <0.00%> (-0.27%)	⬇️
network/wsNetwork.go	64.50% <0.00%> (ø)
ledger/acctupdates.go	64.75% <0.00%> (+0.09%)	⬆️
network/requestTracker.go	71.55% <0.00%> (+0.43%)	⬆️
catchup/service.go	69.82% <0.00%> (+0.74%)	⬆️
ledger/blockqueue.go	82.18% <0.00%> (+1.14%)	⬆️
txnsync/mainloop.go	87.32% <0.00%> (+1.40%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 729e597...c611ba1. Read the comment docs.

[algobarb]

Looks good.