[llvm] [Delinearization] Remove `isKnownNonNegative` (PR #171817)

[Sebastian Pop via llvm-commits]

sebpop wrote:

The code was added in https://reviews.llvm.org/D48481 with a testcase that recently regressed in this commit:
```
commit 05dd957cda663273ae0e5739656ffe701404f37c
Author: Ryotaro Kasuga <kasuga.ryotaro at fujitsu.com>
Date:   Fri Aug 8 10:58:13 2025 +0900

    [DA] Fix the check between Subscript and Size after delinearization (#151326)
[...]
+; FIXME? It seems that we cannot prove that %N is non-negative...
 define void @nonnegative(ptr nocapture %A, i32 %N) {
 ; CHECK-LABEL: 'nonnegative'
 ; CHECK-NEXT:  Src: store i32 1, ptr %arrayidx, align 4 --> Dst: store i32 1, ptr %arrayidx, align 4
-; CHECK-NEXT:    da analyze - none!
+; CHECK-NEXT:    da analyze - output [* *]!
 ; CHECK-NEXT:  Src: store i32 1, ptr %arrayidx, align 4 --> Dst: store i32 2, ptr %arrayidx, align 4
-; CHECK-NEXT:    da analyze - consistent output [0 0|<]!
+; CHECK-NEXT:    da analyze - output [* *|<]!
 ; CHECK-NEXT:  Src: store i32 2, ptr %arrayidx, align 4 --> Dst: store i32 2, ptr %arrayidx, align 4
-; CHECK-NEXT:    da analyze - none!
+; CHECK-NEXT:    da analyze - output [* *]!
```


https://github.com/llvm/llvm-project/pull/171817