Revert "fix protobuf version to 3.20.0 (#6612)" (#6721)

This reverts commit 438917f.

Co-authored-by: Linchenn <[email protected]>

Author: pyu10055

tfjs-converter/python/BUILD

@@ -48,7 +48,6 @@ py_wheel(
     license = "Apache 2.0",
     python_tag = "py3",
     requires = [
-        "protobuf==3.20.0",
         "tensorflow>=2.1.0,<3",
         "six>=1.12.0,<2",
         "tensorflow-hub>=0.7.0,<0.13",

tfjs-converter/python/requirements.txt

@@ -1,4 +1,3 @@
-protobuf==3.20.0
 tensorflow>=2.1.0,<3
 numpy~=1.19.2
 six>=1.12.0,<2