Revert "Add a specialized instruction for `.nil?` calls"

This reverts commit 9faef3113fb4331524b81ba73005ba13fa0ef6c6.

It seemed to cause a failure on macOS Mojave, though I'm unsure how.
https://rubyci.org/logs/rubyci.s3.amazonaws.com/osx1014/ruby-master/log/20190802T034503Z.fail.html.gz

This tentative revert is to check if the issue is actually caused by the
change or not.

1 files changed, 0 insertions, 1 deletions

diff --git a/vm_core.h b/vm_core.h
index d5e18ba489..0120f21831 100644
--- a/vm_core.h
+++ b/vm_core.h
@@ -550,7 +550,6 @@ enum ruby_basic_operators {
     BOP_LENGTH,
     BOP_SIZE,
     BOP_EMPTY_P,
-    BOP_NIL_P,
     BOP_SUCC,
     BOP_GT,
     BOP_GE,