Fix gplan.so: use armv7 binary from official 1.6.6 release

The gplan.so (CAMotics G-code planner) must be a 32-bit ARM binary
matching the Pi's Python 3.5. Source it from the official release
package rather than cross-compiling (SCons ignores CC/CXX overrides).

Also revert install.sh gplan.so preservation logic — simpler to just
ship the correct binary in the package.

setup.py

@@ -17,7 +17,7 @@ setup(
     license = pkg['license'],
     url = pkg['homepage'],
     package_dir = {'': 'src/py'},
-    packages = ['bbctrl', 'inevent', 'lcd', 'camotics','iw_parse'],
+    packages = ['bbctrl', 'inevent', 'lcd', 'camotics', 'iw_parse'],
     include_package_data = True,
     entry_points = {
         'console_scripts': [