fix: misleading help text for 'llama stack build' and 'llama stack run' (#1910)

# What does this PR do?
current text for 'llama stack build' and 'llama stack run' says that if
no argument is passed to '--image-name' that the active Conda
environment will be used

in reality, the active enviroment is used whether it is from conda,
virtualenv, etc.

## Test Plan
N/A

## Documentation
N/A

Signed-off-by: Nathan Weinberg <nweinber@redhat.com>

llama_stack/cli/stack/run.py

@@ -45,7 +45,7 @@ class StackRun(Subcommand):
             "--image-name",
             type=str,
             default=os.environ.get("CONDA_DEFAULT_ENV"),
-            help="Name of the image to run. Defaults to the current conda environment",
+            help="Name of the image to run. Defaults to the current environment",
         )
         self.parser.add_argument(
             "--disable-ipv6",