Drop tests/upper-constraints.txt. (#7073)

tests/upper-constraints.txt

@@ -1,17 +0,0 @@
-# Request the latest known version or newer of some dependencies to prevent the
-# pip dependency resolver from spending too much time backtracking.
-attrs>=20.2.0
-Automat>=0.8.0
-botocore>=1.20.30
-itemadapter>=0.1.1
-itemloaders>=1.0.3
-lxml>=4.6.1
-parsel>=1.5.2
-Pillow>=8.0.1
-pyOpenSSL>=17.5  # mitmproxy 4.0.4
-pytest>=6.2.1
-pytest-twisted>=1.13.1
-service_identity>=17.0.0
-six>=1.14.0
-sybil>=2.0.0
-Twisted>=19.10.0

tox.ini

@@ -41,8 +41,6 @@ passenv =
 download = true
 commands =
     pytest {posargs:--cov-config=pyproject.toml --cov=scrapy --cov-report= --cov-report=term-missing --cov-report=xml --junitxml=testenv.junit.xml -o junit_family=legacy --durations=10 docs scrapy tests --doctest-modules}
-install_command =
-    python -I -m pip install -ctests/upper-constraints.txt {opts} {packages}
 
 [testenv:typing]
 basepython = python3.9
@@ -121,8 +119,6 @@ deps =
     # above, hence we do not install it in pinned environments at the moment
 setenv =
     _SCRAPY_PINNED=true
-install_command =
-    python -I -m pip install {opts} {packages}
 commands =
     ; tests for docs fail with parsel < 1.8.0
     pytest {posargs:--cov-config=pyproject.toml --cov=scrapy --cov-report=xml --cov-report= --junitxml=pinned.junit.xml -o junit_family=legacy --durations=10 scrapy tests}
@@ -132,7 +128,6 @@ basepython = {[pinned]basepython}
 deps =
     {[pinned]deps}
     PyDispatcher==2.0.5
-install_command = {[pinned]install_command}
 setenv =
     {[pinned]setenv}
 commands = {[pinned]commands}
@@ -168,7 +163,6 @@ deps =
     robotexclusionrulesparser==1.6.2
     uvloop==0.14.0; platform_system != "Windows" and implementation_name != "pypy"
     zstandard==0.1; implementation_name != "pypy"
-install_command = {[pinned]install_command}
 setenv =
     {[pinned]setenv}
 commands = {[pinned]commands}
@@ -181,7 +175,6 @@ commands =
 basepython = {[pinned]basepython}
 deps = {[testenv:pinned]deps}
 commands = {[pinned]commands} --reactor=default
-install_command = {[pinned]install_command}
 setenv =
     {[pinned]setenv}
 
@@ -218,7 +211,6 @@ deps =
 commands =
     ; disabling both coverage and docs tests
     pytest {posargs:--durations=10 scrapy tests}
-install_command = {[pinned]install_command}
 setenv =
     {[pinned]setenv}
 
@@ -269,7 +261,6 @@ basepython = {[pinned]basepython}
 deps =
     {[pinned]deps}
     botocore==1.4.87
-install_command = {[pinned]install_command}
 setenv =
     {[pinned]setenv}
 commands =