delete: Remove multistrap as it is no longer needed

multistrap was introduced when mmdebstrap could not be used to build the root filesystem. Now that the project has successfully transitioned to using mmdebstrap, multistrap is redundant.

Changes:
- termux#376
- termux@bb97e3c

bootstrap-rootfs.sh

@@ -10,7 +10,7 @@ if [ "$(uname -o)" = "Android" ]; then
 	exit 1
 fi
 
-for i in curl git jq mmdebstrap sudo tar xz multistrap; do
+for i in curl git jq mmdebstrap sudo tar xz; do
 	if [ -z "$(command -v "$i")" ]; then
 		echo "[!] '$i' is not installed."
 		exit 1