fix core-http changelog (Azure#16116)

The release pipeline complains if there are empty sections in the changelog. Removing the empty section to correct this and unblock core-http release.

Author: maorleger

sdk/core/core-http/CHANGELOG.md

@@ -12,8 +12,6 @@
 
 - Updated @azure/core-tracing to version `1.0.0-preview.12`. See [@azure/core-tracing CHANGELOG](https://github.com/Azure/azure-sdk-for-js/blob/main/sdk/core/core-tracing/CHANGELOG.md) for details about breaking changes with tracing.
 
-### Key Bugs Fixed
-
 ### Fixed
 
 - Fixed an issue where `proxySettings` does not work when there is username but no password [Issue 15720](https://github.com/Azure/azure-sdk-for-js/issues/15720)