revert using backports

`isFALSE()` needed at pkg build time.

Author: t-kalinowski

DESCRIPTION

@@ -38,7 +38,6 @@ Imports:
     methods,
     R6,
     ellipsis,
-    backports,
     rlang
 Suggests:
     ggplot2,

R/metrics.R

@@ -104,6 +104,11 @@ NULL
 NULL
 
 
+if(getRversion() < "3.4.2")
+  isFALSE <- function (x) {
+    is.logical(x) && length(x) == 1L && !is.na(x) && !x
+  }
+
 py_metric_wrapper <- function(py_fn, py_cls, formals=NULL, modifiers=NULL,
                            py_fn_name = TRUE) {
   modifiers <- substitute(modifiers)

R/package.R

@@ -96,8 +96,6 @@ keras <- NULL
 
 .onLoad <- function(libname, pkgname) {
 
-  backports::import(pkgname, "isFALSE")
-
   # resolve the implementation module (might be keras proper or might be tensorflow)
   implementation_module <- resolve_implementation_module()