git: fix index handling of removed files during commit (issue6398)

Other changes in this series also changed the behavior here in
positive ways, but this was the final step that actually fixed things.

Differential Revision: https://phab.mercurial-scm.org/D8999

hgext/git/dirstate.py

@@ -303,8 +303,10 b' class gitdirstate(object):'
     def drop(self, f):
         index = self.git.index
         index.read()
-        index.remove(pycompat.fsdecode(f))
-        index.write()
+        fs = pycompat.fsdecode(f)
+        if fs in index:
+            index.remove(fs)
+            index.write()
 
     def remove(self, f):
         index = self.git.index

tests/test-git-interop.t

@@ -270,3 +270,8 b' This covers manifest.diff()'
   +++ b/beta	Mon Jan 01 00:00:11 2007 +0000
   @@ -0,0 +1,1 @@
   +beta
+
+
+Deleting files should also work (this was issue6398)
+  $ hg rm beta
+  $ hg ci -m 'remove beta'