Win flex-bison and Chocolatey updates.

Chocolatey's latest winflexbison package is usable. Update
config.nmake, FindLEX.cmake, and FindYACC.cmake accordingly.  Rename
CHOCOLATEY_INSTALL_PATH to CHOCOLATEY_BIN_PATH since that's what we're
finding.

Change-Id: I39973fba0531b3f7a1315ca010a8bd70581db3fb
Reviewed-on: https://code.wireshark.org/review/3479
Reviewed-by: Gerald Combs <gerald@wireshark.org>