Cleanup executable status on src files.

[philljj]

These two src files had executable permissions:

$ find * -type f -executable | grep "\.[c,h]"
examples/wiot/wiot.h
examples/multithread/multithread.c

$ ls -l examples/wiot/wiot.h 
-rwxrwxr-x 1 jordan jordan 1122 Nov 22 10:52 examples/wiot/wiot.h
$ ls -l examples/multithread/multithread.c 
-rwxrwxr-x 1 jordan jordan 25332 Nov 22 10:52 examples/multithread/multithread.c

This PR fixes them:

$ find * -type f -executable | grep "\.[c,h]"

$ ls -l examples/wiot/wiot.h
-rw-rw-r-- 1 jordan jordan 1122 Nov 22 10:57 examples/wiot/wiot.h
$ ls -l examples/multithread/multithread.c 
-rw-rw-r-- 1 jordan jordan 25332 Nov 22 10:57 examples/multithread/multithread.c