cmd/link: remove unused SFILEPATH symbol kind

Last reference appears to have been removed in CL 227759.

Change-Id: Ieb9da0a69a8beb96dcb5309ca43cf1df61d39bce
Reviewed-on: https://go-review.googlesource.com/c/go/+/715541
Auto-Submit: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Than McIntosh <thanm@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>

Author: ianlancetaylor

src/cmd/link/internal/sym/symkind.go

@@ -130,7 +130,6 @@ const (
 	SMACHOSYMTAB      // Mach-O symbol table.
 	SMACHOINDIRECTPLT // Mach-O indirect PLT.
 	SMACHOINDIRECTGOT // Mach-O indirect GOT.
-	SFILEPATH         // Unused?
 	SDYNIMPORT        // Reference to symbol defined in shared library.
 	SHOSTOBJ          // Symbol defined in non-Go object file.
 	SUNDEFEXT         // Undefined symbol for resolution by external linker.