Remove DHCP lease expiry code.
Remove DHCP lease expiry code.

Fixes #325.

timami/stratux,cyoung/stratux,timami/stratux,timami/stratux,lukepalmer/stratux,westphae/stratux,timami/PlaneSense,ccicchitelli/stratux,egid/stratux,lukepalmer/stratux,cyoung/stratux,cyoung/stratux,ccicchitelli/stratux,egid/stratux,jpoirier/stratux,lukepalmer/stratux,westphae/stratux,lukepalmer/stratux,lukepalmer/stratux,kdknigga/stratux,cyoung/stratux,timami/stratux,ssokol/stratux,westphae/stratux,kdknigga/stratux,timami/stratux,stratux-fork/stratux,kdknigga/stratux,ssokol/stratux,timami/PlaneSense,kdknigga/stratux,lukepalmer/stratux,jpoirier/stratux,timami/stratux,ccicchitelli/stratux,stratux-fork/stratux,stratux-fork/stratux,ssokol/stratux,timami/PlaneSense,stratux-fork/stratux,westphae/stratux,ssokol/stratux,egid/stratux,westphae/stratux,jpoirier/stratux,westphae/stratux,kdknigga/stratux,timami/PlaneSense,cyoung/stratux,ccicchitelli/stratux,jpoirier/stratux,timami/PlaneSense,egid/stratux,jpoirier/stratux,ccicchitelli/stratux,jpoirier/stratux,kdknigga/stratux,stratux-fork/stratux,ssokol/stratux,ccicchitelli/stratux,cyoung/stratux,egid/stratux,egid/stratux,ssokol/stratux,stratux-fork/stratux,timami/PlaneSense