Remove unused exists_file/1

This is not used by the compiler and is disabled
when running inside Gerrit Code Review.

Change-Id: I76c2d52cb8ecc7c647702b352daa7936cc0edc0d

src/builtin/PRED_exists_file_1.java

diff --git a/src/builtin/PRED_exists_file_1.java b/src/builtin/PRED_exists_file_1.java
deleted file mode 100644
index 1aaebc0..0000000
--- a/src/builtin/PRED_exists_file_1.java
+++ /dev/null
@@ -1,36 +0,0 @@
-package com.googlecode.prolog_cafe.builtin;
-
-import com.googlecode.prolog_cafe.lang.IllegalDomainException;
-import com.googlecode.prolog_cafe.lang.Operation;
-import com.googlecode.prolog_cafe.lang.PInstantiationException;
-import com.googlecode.prolog_cafe.lang.Predicate;
-import com.googlecode.prolog_cafe.lang.Prolog;
-import com.googlecode.prolog_cafe.lang.PrologException;
-import com.googlecode.prolog_cafe.lang.SymbolTerm;
-import com.googlecode.prolog_cafe.lang.Term;
-
-import java.io.File;
-
-/** {@code exists_file(+File)} */
-public class PRED_exists_file_1 extends Predicate.P1 {
-  public PRED_exists_file_1(Term a1, Operation next) {
-    arg1 = a1;
-    cont = next;
-  }
-
-  @Override
-  public Operation exec(Prolog engine) throws PrologException {
-    engine.requireFeature(Prolog.Feature.IO, this, arg1);
-    engine.setB0();
-
-    Term a1 = arg1.dereference();
-    if (a1.isVariable()) throw new PInstantiationException(this, 1);
-    if (!a1.isSymbol()) throw new IllegalDomainException(this, 1, "file", a1);
-
-    File file = new File(a1.name());
-    if (file.isFile())
-      return cont;
-    else
-      return engine.fail();
-  }
-}