remove pin (#300)

For testing, deployed 3.7 + 3.9 on long running instances. Calling
console apis to update flags/config and checking that gcir is being
updated to the same lcut as the grpc response lcut.

Python 3.7 has the following restrictions:
**grpcio==1.51.1 **
**protobuf<4.0.0,>=3.2.0 **
<img width="520" alt="Screenshot 2024-08-19 at 11 51 47 AM"
src="https://github.com/user-attachments/assets/c1b37112-eefc-4bdc-9967-592bb591d66a">

Tested Python 3.9 with the same restrictions as well as no restriction:
<img width="647" alt="Screenshot 2024-08-19 at 11 52 34 AM"
src="https://github.com/user-attachments/assets/c82abfe4-f5e7-492c-b160-cf5127b031d5">

setup.py

@@ -37,12 +37,12 @@
         'requests',
         'ua_parser',
         'ip3country',
-        'grpcio==1.62.3',
-        'protobuf==4.24.4',
+        'grpcio',
+        'protobuf',
     ],
     tests_require=test_deps,
     extras_require=extras,
     include_package_data=True,
     packages=find_packages(include=['statsig', 'statsig.grpc', 'statsig.grpc.generated']),
-    python_requires='>=3.5',
+    python_requires='>=3.7',
 )