Remove dependencies not needed to run tests.

--- httpx-0.28.1/requirements.txt.orig
+++ httpx-0.28.1/requirements.txt
@@ -2,21 +2,12 @@
 # On the other hand, we're not pinning package dependencies, because our tests
 # needs to pass with the latest version of the packages.
 # Reference: https://github.com/encode/httpx/pull/1721#discussion_r661241588
--e .[brotli,cli,http2,socks,zstd]
+.[socks,zstd]
 
 # Optional charset auto-detection
 # Used in our test cases
 chardet==5.2.0
 
-# Documentation
-mkdocs==1.6.1
-mkautodoc==0.2.0
-mkdocs-material==9.5.47
-
-# Packaging
-build==1.2.2.post1
-twine==6.0.1
-
 # Tests & Linting
 coverage[toml]==7.6.1
 cryptography==44.0.0