in-tree-build is now the default in pip

Author: Julian

tox.ini

@@ -24,10 +24,9 @@ whitelist_externals =
 commands =
     {envpython} -m pip install 'pip>=21.1.1'  # Evade CVE-2021-28363
 
-    # Remove once pypa/pip#7555 is closed.
-    noextra: {envpython} -m pip install --use-feature=in-tree-build {toxinidir}
-    format,perf: {envpython} -m pip install  --use-feature=in-tree-build '{toxinidir}[format]'
-    format_nongpl: {envpython} -m pip install --use-feature=in-tree-build '{toxinidir}[format_nongpl]'
+    noextra: {envpython} -m pip install {toxinidir}
+    format,perf: {envpython} -m pip install '{toxinidir}[format]'
+    format_nongpl: {envpython} -m pip install '{toxinidir}[format_nongpl]'
 
     tests,coverage,codecov: {envpython} -m {env:MAYBE_COVERAGE:} twisted.trial {posargs:jsonschema}
     tests: {envpython} -m doctest {toxinidir}/README.rst