chore(generator): remove unnecessary session.install('-e', '../google-api-core') from noxfile.py

Author: hebaalazzeh

packages/gapic-generator/noxfile.py

@@ -248,10 +248,6 @@ def showcase_library(
 
     # Install gapic-generator-python
     session.install("-e", ".")
-    # Install local editable google-api-core for monorepo development testing.
-    # On Python 3.10 below, google-api-core<2.28 is installed to validate
-    # fallback compatibility against released versions of google-api-core.
-    session.install("-e", "../google-api-core")
 
     # Install grpcio-tools for protoc
     session.install("grpcio-tools")