[BUG]: Removed defaulting HttpClient headers to empty dict (#1329)

Refs: #1302

## Description of changes

*Summarize the changes made by this PR.*
 - Improvements & Bug fixes
- Removed defaulting of headers for HttpClient as this causes
differences in settings when clients are initialized from HttpClient and
Client with the same settings which raises an error

## Test plan
*How are these changes tested?*

- [x] Tests pass locally with `pytest` for python

## Documentation Changes
N/A

chromadb/__init__.py

@@ -160,8 +160,6 @@ def HttpClient(
         database: The database to use for this client. Defaults to the default database.
     """
 
-    if headers is None:
-        headers = {}
     if settings is None:
         settings = Settings()