Fix flake8 whitespace reports

$ flake8 | grep -E '(E128|E203|E221|E226|E303|W291|W293)'
./mesonbuild/backend/backends.py:32:1: E303 too many blank lines (3)
./mesonbuild/modules/i18n.py:90:56: E128 continuation line under-indented for visual indent

mesonbuild/backend/backends.py

@@ -28,7 +28,6 @@ from collections import OrderedDict
 import shlex
 
 
-
 class CleanTrees:
     '''
     Directories outputted by custom targets that have to be manually cleaned

mesonbuild/modules/i18n.py

@@ -87,7 +87,7 @@ class I18nModule(ExtensionModule):
         else:
             if isinstance(inputfile, str):
                 inputfile = mesonlib.File.from_source_file(state.environment.source_dir,
-                                                       state.subdir, inputfile)
+                                                           state.subdir, inputfile)
             output = kwargs['output']
             ifile_abs = inputfile.absolute_path(state.environment.source_dir,
                                                 state.environment.build_dir)