removed old original SPIRV-Tools submodule

Author: AnastaZIuk

.gitmodules

@@ -1,9 +1,6 @@
 [submodule "external/SPIRV-Headers"]
 	path = external/SPIRV-Headers
 	url = https://github.com/KhronosGroup/SPIRV-Headers
-[submodule "external/SPIRV-Tools"]
-	path = external/SPIRV-Tools
-	url = https://github.com/KhronosGroup/SPIRV-Tools
 [submodule "external/googletest"]
 	path = external/googletest
 	url = https://github.com/google/googletest