Instead, use a hard-coded map of licenses.
Hardcode a false dependency on diff-match-patch to avoid a diff for
the Apache2.0 license.
Tested:
bazel build Documentation:js_licenses.txt
buck build Documentation:js_licenses.txt
diff -u buck-out/gen/Documentation/js_licenses.txt/js_licenses.txt \
bazel-genfiles/Documentation/js_licenses.txt
diff shows only diffs for added [[header]] anchors.
Change-Id: I7886e1fadec900cf854a1b3b7c538b83d66af7a4