pkg/strconv: remove CanBackquote

This function doesn't make sense in CUE, as it
has no backquoted strings.

Change-Id: I12a2d0c920c3e68277c00529abda49ec01d2389a
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/2683
Reviewed-by: Marcel van Lohuizen <[email protected]>

Author: mpvl

cue/builtins.go

@@ -16,7 +16,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:generate qgo -exclude=Append,Unquote,Itoa extract strconv
+//go:generate qgo -exclude=Append,Unquote,Itoa,CanBackquote extract strconv
 
 package strconv
 
@@ -174,13 +174,6 @@ func QuoteRuneToGraphic(r rune) string {
 	return strconv.QuoteRuneToGraphic(r)
 }
 
-// CanBackquote reports whether the string s can be represented
-// unchanged as a single-line backquoted string without control
-// characters other than tab.
-func CanBackquote(s string) bool {
-	return strconv.CanBackquote(s)
-}
-
 // IsPrint reports whether the rune is defined as printable by Go, with
 // the same definition as unicode.IsPrint: letters, numbers, punctuation,
 // symbols and ASCII space.