pkg/path: remove osInfo.HasPrefix

We seem to have imported this deprecated API from Go back in 2020,
when that was entirely unnecessary at the time.
We don't have any tests nor documentation for it.

The good news is that we never exported any of the OS types in Go,
nor did we expose a HasPrefix func for CUE importers
like we did with IsAbs and others.

Hence, I assume this is an entirely backwards compatible change.

Signed-off-by: Daniel Martí <[e-mail]>
Change-Id: I2a23d4aa7d88678ae922d579b9f68a21c6d60f72
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1230077
Unity-Result: CUE porcuepine <[e-mail]>
Reviewed-by: Matthew Sackman <[e-mail]>
TryBot-Result: CUEcueckoo <[e-mail]>

pkg/path/os.go

···
 	splitList(path string) []string
 	volumeNameLen(path string) int
 	IsAbs(path string) (b bool)
-	HasPrefix(p, prefix string) bool
 	join(elem []string) string
 	sameWord(a, b string) bool
 }

pkg/path/path_nix.go

···
 	return 0
 }
 
-// HasPrefix exists for historical compatibility and should not be used.
-//
-// Deprecated: HasPrefix does not respect path boundaries and
-// does not ignore case when required.
-func (o unixInfo) HasPrefix(p, prefix string) bool {
-	return strings.HasPrefix(p, prefix)
-}
-
 func (o unixInfo) splitList(path string) []string {
 	if path == "" {
 		return []string{}

pkg/path/path_p9.go

···
 	return 0
 }
 
-// HasPrefix exists for historical compatibility and should not be used.
-//
-// Deprecated: HasPrefix does not respect path boundaries and
-// does not ignore case when required.
-func (o plan9Info) HasPrefix(p, prefix string) bool {
-	return strings.HasPrefix(p, prefix)
-}
-
 func (o plan9Info) splitList(path string) []string {
 	if path == "" {
 		return []string{}

pkg/path/path_win.go

···
 	return 0
 }
 
-// HasPrefix exists for historical compatibility and should not be used.
-//
-// Deprecated: HasPrefix does not respect path boundaries and
-// does not ignore case when required.
-func (os windowsInfo) HasPrefix(p, prefix string) bool {
-	if strings.HasPrefix(p, prefix) {
-		return true
-	}
-	return strings.HasPrefix(strings.ToLower(p), strings.ToLower(prefix))
-}
-
 func (os windowsInfo) splitList(path string) []string {
 	// The same implementation is used in LookPath in os/exec;
 	// consider changing os/exec when changing this.