scripts: Reverted del to resolve shadowed builtins

I don't know how I completely missed that this doesn't actually work!

Using del _does_ work in Python's repl, but it makes sense the repl may
differ from actual function execution in this case.

The problem is Python still thinks the relevant builtin is a local
variables after deletion, raising an UnboundLocalError instead of
performing a global lookup. In theory this would work if the variable
could be made global, but since global/nonlocal statements are lifted,
Python complains with "SyntaxError: name 'list' is parameter and
global".

And that's A-Ok! Intentionally shadowing language builtins already puts
this code deep into ugly hacks territory.

scripts/dbgbmap.py

@@ -2964,7 +2964,8 @@ class Lfs:
     # lookup operations 
     def lookup(self, mid, mdir=None, *,
             all=False):
-        all_ = all; del all
+        import builtins
+        all_, all = all, builtins.all
 
         # is this mid grmed?
         if not all_ and self.grmed(mid):
@@ -2985,7 +2986,8 @@ class Lfs:
 
     def namelookup(self, did, name, *,
             all=False):
-        all_ = all; del all
+        import builtins
+        all_, all = all, builtins.all
 
         mid_, mdir_, name_ = self.mtree.namelookup(did, name)
         if mid_ is None:
@@ -3047,7 +3049,8 @@ class Lfs:
             all=False,
             path=False,
             depth=None):
-        all_ = all; del all
+        import builtins
+        all_, all = all, builtins.all
 
         # default to the root directory
         if path_ is None:
@@ -3100,7 +3103,8 @@ class Lfs:
             all=False,
             path=False,
             depth=None):
-        all_ = all; del all
+        import builtins
+        all_, all = all, builtins.all
 
         # default to the root directory
         did = did or self.root.did
@@ -3155,7 +3159,8 @@ class Lfs:
 
     def orphans(self,
             all=False):
-        all_ = all; del all
+        import builtins
+        all_, all = all, builtins.all
 
         # first find all reachable dids
         dids = {self.root.did}