External libs - update linux build externals script

This brings the script into line with previous changes made by Sam.

Author: ethancrawford

app/external/linux_build_externals.sh

@@ -13,7 +13,4 @@ cmake -DERLANG_INCLUDE_PATH=${ERLANG_INCLUDE_PATH} -G "Unix Makefiles" ..
 echo "Building external deps..."
 cmake --build . --config Release
 
-echo "Building supercollider-plugins..."
-cmake --build . --target supercollider-plugins
-
 cd "${SCRIPT_DIR}"