Fix flake8 'imported but unused' reports

$ flake8 | grep F401
./mesonbuild/minstall.py:15:1: F401 'gzip' imported but unused
./mesonbuild/backend/backends.py:26:1: F401 '..compilers.get_macos_dylib_install_name' imported but unused
./mesonbuild/backend/backends.py:29:1: F401 'functools.lru_cache' imported but unused
./mesonbuild/scripts/dist.py:27:1: F401 'mesonbuild.dependencies.ExternalProgram' imported but unused

mesonbuild/backend/backends.py

@@ -23,10 +23,9 @@ import subprocess
 from ..mesonlib import MesonException, OrderedSet
 from ..mesonlib import classify_unity_sources
 from ..mesonlib import File
-from ..compilers import CompilerArgs, get_macos_dylib_install_name
+from ..compilers import CompilerArgs
 from collections import OrderedDict
 import shlex
-from functools import lru_cache
 
 
 

mesonbuild/minstall.py

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import sys, pickle, os, shutil, subprocess, gzip, errno
+import sys, pickle, os, shutil, subprocess, errno
 import shlex
 from glob import glob
 from .scripts import depfixer

mesonbuild/scripts/dist.py

@@ -24,7 +24,6 @@ import tarfile, zipfile
 import tempfile
 from glob import glob
 from mesonbuild.environment import detect_ninja
-from mesonbuild.dependencies import ExternalProgram
 from mesonbuild.mesonlib import windows_proof_rmtree
 from mesonbuild import mlog