Remove unused requirement_set in commands

src/pip/_internal/commands/download.py

@@ -9,7 +9,6 @@ import os
 from pip._internal.cli import cmdoptions
 from pip._internal.cli.cmdoptions import make_target_python
 from pip._internal.cli.req_command import RequirementCommand, with_cleanup
-from pip._internal.req import RequirementSet
 from pip._internal.req.req_tracker import get_requirement_tracker
 from pip._internal.utils.misc import ensure_dir, normalize_path, write_output
 from pip._internal.utils.temp_dir import TempDirectory
@@ -102,8 +101,6 @@ class DownloadCommand(RequirementCommand):
         with get_requirement_tracker() as req_tracker, TempDirectory(
             options.build_dir, delete=build_delete, kind="download"
         ) as directory:
-
-            requirement_set = RequirementSet()
             reqs = self.populate_requirement_set(
                 args,
                 options,

src/pip/_internal/commands/install.py

@@ -30,7 +30,7 @@ from pip._internal.exceptions import (
 )
 from pip._internal.locations import distutils_scheme
 from pip._internal.operations.check import check_install_conflicts
-from pip._internal.req import RequirementSet, install_given_reqs
+from pip._internal.req import install_given_reqs
 from pip._internal.req.req_tracker import get_requirement_tracker
 from pip._internal.utils.deprecation import deprecated
 from pip._internal.utils.distutils_args import parse_distutils_args
@@ -291,10 +291,6 @@ class InstallCommand(RequirementCommand):
         with get_requirement_tracker() as req_tracker, TempDirectory(
             options.build_dir, delete=build_delete, kind="install"
         ) as directory:
-            requirement_set = RequirementSet(
-                check_supported_wheels=not options.target_dir,
-            )
-
             try:
                 reqs = self.populate_requirement_set(
                     args, options, finder, session,

src/pip/_internal/commands/wheel.py

@@ -13,7 +13,6 @@ from pip._internal.cache import WheelCache
 from pip._internal.cli import cmdoptions
 from pip._internal.cli.req_command import RequirementCommand, with_cleanup
 from pip._internal.exceptions import CommandError, PreviousBuildDirError
-from pip._internal.req import RequirementSet
 from pip._internal.req.req_tracker import get_requirement_tracker
 from pip._internal.utils.misc import ensure_dir, normalize_path
 from pip._internal.utils.temp_dir import TempDirectory
@@ -128,9 +127,6 @@ class WheelCommand(RequirementCommand):
         with get_requirement_tracker() as req_tracker, TempDirectory(
             options.build_dir, delete=build_delete, kind="wheel"
         ) as directory:
-
-            requirement_set = RequirementSet()
-
             try:
                 reqs = self.populate_requirement_set(
                     args, options, finder, session,