[AVR] Remove the select-mbb-placement-bug.ll test

This test was originally added when an old bug was fixed that caused
broken iterator code to break basic block placement.

The issue has an extremely low chance of every being a problem again.

This specific test is very flaky and fails often due to upstream
changes.

I have removed this test because it negates more value than it returns.

llvm-svn: 318134

llvm/test/CodeGen/AVR/select-mbb-placement-bug.ll

@@ -1,35 +0,0 @@
-; RUN: llc -mcpu=atmega328p < %s -march=avr | FileCheck %s
-
-; CHECK-LABEL: loopy
-define internal fastcc void @loopy() {
-
-; In this case, when we expand `Select8`/`Select16`, we should be
-; replacing the existing MBB instead of adding a new one.
-;
-; https://github.com/avr-rust/rust/issues/49
-
-; CHECK: LBB0_{{[0-9]+}}:
-; CHECK: LBB0_{{[0-9]+}}:
-; CHECK-NOT: LBB0_{{[0-9]+}}:
-start:
-  br label %bb7.preheader
-
-bb7.preheader:                                    ; preds = %bb10, %start
-  %i = phi i8 [ 0, %start ], [ %j, %bb10 ]
-  %j = phi i8 [ 1, %start ], [ %next, %bb10 ]
-  br label %bb10
-
-bb4:                                              ; preds = %bb10
-  ret void
-
-bb10:                                             ; preds = %bb7.preheader
-  tail call fastcc void @observe(i8 %i, i8 1)
-  %0 = icmp ult i8 %j, 20
-  %1 = zext i1 %0 to i8
-  %next = add i8 %j, %1
-  br i1 %0, label %bb7.preheader, label %bb4
-
-}
-
-declare void @observe(i8, i8);
-