Revise the deprecation logging

This introduces a more automatic way of increasing the log levels for deprecation log statements based on the version it was deprecated.

The thresholds are a little arbitrary, but

* We log INFO for 6 releases
* We log WARN for another 6 releases
* THen ERROR (failing the build)

This should give theme authors plenty of time to catch up without having the log filled with warnings.

helpers/general.go

@@ -27,9 +27,6 @@ import (
 	"unicode"
 	"unicode/utf8"
 
-	"github.com/gohugoio/hugo/common/hugo"
-	"github.com/gohugoio/hugo/common/loggers"
-
 	"github.com/spf13/afero"
 
 	"github.com/jdkato/prose/transform"
@@ -246,19 +243,6 @@ func compareStringSlices(a, b []string) bool {
 	return true
 }
 
-// Deprecated informs about a deprecation, but only once for a given set of arguments' values.
-// If the err flag is enabled, it logs as an ERROR (will exit with -1) and the text will
-// point at the next Hugo release.
-// The idea is two remove an item in two Hugo releases to give users and theme authors
-// plenty of time to fix their templates.
-func Deprecated(item, alternative string, err bool) {
-	if err {
-		loggers.Log().Errorf("%s is deprecated and will be removed in Hugo %s. %s", item, hugo.CurrentVersion.Next().ReleaseVersion(), alternative)
-	} else {
-		loggers.Log().Warnf("%s is deprecated and will be removed in a future release. %s", item, alternative)
-	}
-}
-
 // SliceToLower goes through the source slice and lowers all values.
 func SliceToLower(s []string) []string {
 	if s == nil {