chore: Rm v2 suffixes (#929)

Author: hinthornw

docs/evaluation/how_to_guides/vitest_jest.mdx

@@ -315,7 +315,7 @@ Create a `.env` file with your `OPENAI_API_KEY` and LangSmith credentials if you
 OPENAI_API_KEY="YOUR_KEY_HERE"
 
 LANGSMITH_API_KEY="YOUR_LANGSMITH_KEY"
-LANGSMITH_TRACING_V2="true"
+LANGSMITH_TRACING="true"
 ```
 
 Now use the `eval` script we set up in the previous step to run the test:

docs/observability/how_to_guides/toubleshooting_variable_caching.mdx

@@ -16,7 +16,7 @@ First, check that the environment variables are set correctly by running:
 import os
 
 print(os.getenv("LANGSMITH_PROJECT"))
-print(os.getenv("LANGSMITH_TRACING_V2"))
+print(os.getenv("LANGSMITH_TRACING"))
 print(os.getenv("LANGSMITH_ENDPOINT"))
 print(os.getenv("LANGSMITH_API_KEY"))
 ```