test_project.py: remove invalid tests

The diff and status commands with extra arguments never worked.
Remove the invalid test cases for them. The next patch is going to
fail this sort of invocation with an error instead of silently
ignoring it.

Signed-off-by: Marti Bolivar <marti.bolivar@nordicsemi.no>

tests/test_project.py

@@ -127,7 +127,6 @@ def test_diff(west_init_tmpdir):
     cmd('diff')
 
     cmd('update Kconfiglib')
-    cmd('diff --cached')  # Pass a custom flag too
 
 
 def test_status(west_init_tmpdir):
@@ -143,7 +142,6 @@ def test_status(west_init_tmpdir):
     cmd('status')
 
     cmd('update Kconfiglib')
-    cmd('status --long')  # Pass a custom flag too
 
 
 def test_forall(west_init_tmpdir):