Revert "[flang] Adjust semantics of the char length of an array constructor" (#98612)

Reverts #97337

This has caused llvm test suite failures on our bots, for example:
https://lab.llvm.org/buildbot/#/builders/17/builds/709

```
FAIL: test-suite::gfortran-regression-execute-regression__char_length_21_f90.test 
FAIL: test-suite::gfortran-regression-execute-regression__char_length_20_f90.test
```

Author: DavidSpickett

flang/lib/Semantics/expression.cpp

@@ -1584,8 +1584,7 @@ class ArrayConstructorContext {
   std::optional<Expr<SubscriptInteger>> LengthIfGood() const {
     if (type_) {
       auto len{type_->LEN()};
-      if (explicitType_ ||
-          (len && IsConstantExpr(*len) && !ContainsAnyImpliedDoIndex(*len))) {
+      if (len && IsConstantExpr(*len) && !ContainsAnyImpliedDoIndex(*len)) {
         return len;
       }
     }

flang/test/Lower/HLFIR/array-ctor-character.f90

@@ -93,11 +93,10 @@ subroutine test_set_length_sanitize(i, c1)
   call takes_char([character(len=i):: c1])
 end subroutine
 ! CHECK-LABEL:   func.func @_QPtest_set_length_sanitize(
-! CHECK:   %[[VAL_2:.*]]:2 = hlfir.declare {{.*}}Ec1
-! CHECK:   %[[VAL_3:.*]]:2 = hlfir.declare %arg0
-! CHECK:   %[[VAL_4:.*]] = fir.load %[[VAL_3]]#0 : !fir.ref<i64>
-! CHECK:   %[[VAL_25:.*]] = fir.load %[[VAL_3]]#0 : !fir.ref<i64>
+! CHECK:   %[[VAL_6:.*]]:2 = hlfir.declare {{.*}}Ec1
+! CHECK:   %[[VAL_9:.*]]:2 = hlfir.declare {{.*}}Ei
+! CHECK:   %[[VAL_25:.*]] = fir.load %[[VAL_9]]#0 : !fir.ref<i64>
 ! CHECK:   %[[VAL_26:.*]] = arith.constant 0 : i64
 ! CHECK:   %[[VAL_27:.*]] = arith.cmpi sgt, %[[VAL_25]], %[[VAL_26]] : i64
 ! CHECK:   %[[VAL_28:.*]] = arith.select %[[VAL_27]], %[[VAL_25]], %[[VAL_26]] : i64
-! CHECK:   %[[VAL_29:.*]] = hlfir.set_length %[[VAL_2]]#0 len %[[VAL_28]] : (!fir.boxchar<1>, i64) -> !hlfir.expr<!fir.char<1,?>>
+! CHECK:   %[[VAL_29:.*]] = hlfir.set_length %[[VAL_6]]#0 len %[[VAL_28]] : (!fir.boxchar<1>, i64) -> !hlfir.expr<!fir.char<1,?>>

flang/test/Semantics/array-constr-len.f90

@@ -10,5 +10,6 @@ subroutine subr(s,n)
   print *, [(s(1:j),j=1,0)]
   print *, [(s(1:1),j=1,0)] ! ok
   print *, [character(2)::(s(1:n),j=1,0)] ! ok
+  !ERROR: Array constructor implied DO loop has no iterations and indeterminate character length
   print *, [character(n)::(s(1:n),j=1,0)]
 end