EmulatorPkg: Remove UNIX_SEC_BUILD/WIN_SEC_BUILD

EmulatorPkg: Remove UNIX_SEC_BUILD/WIN_SEC_BUILD

https://bugzilla.tianocore.org/show_bug.cgi?id=2055

Remove the use of the defines UNIX_SEC_BUILD and
WIN_SEC_BUILD.  This simplifies the build command
for the EmulatorPkg.  Instead, use !if statements
in the DSC file using $(ARCH) and $(FAMILY) to
determine if the build is for a Windows or POSIX
environment.

The Readme.md, BAT, and sh files are also updated
to remove the use of these defines.

Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Andrew Fish <afish@apple.com>
Cc: Ray Ni <ray.ni@intel.com>
Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Hao A Wu <hao.a.wu@intel.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Tested-by: Andrew Fish <afish@apple.com>