Revert "internal/core/adt: carry over enclosing scope"

This reverts https://cuelang.org/cl/1214849,
as it broke two cuelang.org/docs guides as reported in #3924.

Fixes #3924.
Causes #3920 to reopen, as we are reverting the fix.

Signed-off-by: Daniel Martí <[email protected]>
Change-Id: I61ed91546510bb519e2f19616ea928c318fcc6fb
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1215074
TryBot-Result: CUEcueckoo <[email protected]>
Reviewed-by: Marcel van Lohuizen <[email protected]>

Author: mvdan

cue/testdata/cycle/builtins.txtar

@@ -265,8 +265,8 @@ Unifications: 399
 Conjuncts:    731
 Disjuncts:    38
 
-CloseIDElems: 150
-NumCloseIDs: 191
+CloseIDElems: 116
+NumCloseIDs: 189
 -- diff/-out/evalalpha/stats<==>+out/eval/stats --
 diff old new
 --- old
@@ -291,8 +291,8 @@ diff old new
 +Conjuncts:    731
 +Disjuncts:    38
 +
-+CloseIDElems: 150
-+NumCloseIDs: 191
++CloseIDElems: 116
++NumCloseIDs: 189
 -- out/eval/stats --
 Leaks:  25
 Freed:  446

cue/testdata/cycle/chain.txtar

@@ -1705,7 +1705,7 @@ Unifications: 931
 Conjuncts:    4994
 Disjuncts:    1615
 
-CloseIDElems: 19418
+CloseIDElems: 20484
 NumCloseIDs: 1535
 -- diff/-out/evalalpha/stats<==>+out/eval/stats --
 diff old new
@@ -1731,7 +1731,7 @@ diff old new
 +Conjuncts:    4994
 +Disjuncts:    1615
 +
-+CloseIDElems: 19418
++CloseIDElems: 20484
 +NumCloseIDs: 1535
 -- out/eval/stats --
 Leaks:  56

cue/testdata/cycle/inline.txtar

@@ -405,8 +405,8 @@ Unifications: 253
 Conjuncts:    639
 Disjuncts:    0
 
-CloseIDElems: 363
-NumCloseIDs: 231
+CloseIDElems: 329
+NumCloseIDs: 229
 -- diff/-out/evalalpha/stats<==>+out/eval/stats --
 diff old new
 --- old
@@ -431,8 +431,8 @@ diff old new
 +Conjuncts:    639
 +Disjuncts:    0
 +
-+CloseIDElems: 363
-+NumCloseIDs: 231
++CloseIDElems: 329
++NumCloseIDs: 229
 -- out/eval/stats --
 Leaks:  286
 Freed:  253