main: Stop setting GOMAXPROCS to NumCPU explicitly (#1096)
main: Stop setting GOMAXPROCS to NumCPU explicitly (#1096)

GOMAXPROCS will be set automatically after Go 1.5. The minimum version
supported at the moment is 1.9, so setting GOMAXPROCS to NumCPU is not
necessary anymore.

References
https://docs.google.com/document/d/1At2Ls5_fhJQ59kDK2DFVhFu3g5mATSXqqV5QrxinasI/edit
https://tip.golang.org/doc/go1.5#introduction
LightningNetwork/lnd,aakselrod/lnd,LightningNetwork/lnd,aakselrod/lnd