subprojects: Remove unused span-lite

Change-Id: I74896f92263a270a23bec75cd57bb74cb58e49a5
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/subprojects/span-lite.wrap b/subprojects/span-lite.wrap
deleted file mode 100644
index ee0f0db..0000000
--- a/subprojects/span-lite.wrap
+++ /dev/null
@@ -1,3 +0,0 @@
-[wrap-git]
-url = https://github.com/martinmoene/span-lite
-revision = HEAD