Removing Teensy SDK Folder

Fixing Github GUI error "fatal: no submodule mapping found in
.gitmodules for path 'teensy-sdk'"

diff --git a/teensy-sdk b/teensy-sdk
deleted file mode 160000 (submodule)
index 19892c1..0000000
--- a/teensy-sdk
+++ /dev/null
@@ -1 +0,0 @@
-Subproject commit 19892c196894e6676fa69c732e05a03a68d5cb07