Revert "Pin python-rapidjson in cirq-rigetti. (#5666)"

This reverts commit 3e34f5d.

Author: vtomole

cirq-rigetti/requirements.txt

@@ -9,8 +9,6 @@ pydantic~=1.8.2
 pyjwt~=1.7.1
 pyquil~=2.28.2; python_version < "3.7"
 pyquil~=3.0.0; python_version >= "3.7"
-# Remove once https://github.com/python-rapidjson/python-rapidjson/issues/166 is resolved.
-python-rapidjson<=1.6
 python-dateutil~=2.8.1
 qcs-api-client~=0.8.0
 retrying~=1.3.3