Remove serial_link .gitignore and .gitmodules

quantum/serial_link/.gitignore

@@ -1 +0,0 @@
-*.stackdump

quantum/serial_link/.gitmodules

@@ -1,3 +0,0 @@
-[submodule "cgreen/cgreen"]
-	path = cgreen/cgreen
-	url = http://github.com/cgreen-devs/cgreen