fix submodule

Author: DmitriyMusatkin

.gitmodules

@@ -31,7 +31,6 @@
 [submodule "crt/aws-c-s3"]
 	path = crt/aws-c-s3
 	url = git@github.com:awslabs/aws-c-s3.git
-	branch = xxhash
 [submodule "aws-lc"]
 	path = crt/aws-lc
 	url = https://github.com/awslabs/aws-lc.git