6l: remove mention of -e flag

Emitting ELF symbol table is the default behavior now
and cannot be disabled.

R=golang-dev, iant
CC=golang-dev
https://golang.org/cl/5319050

src/cmd/6l/doc.go

@@ -25,9 +25,6 @@ Options new in this version:
 	Elide the dynamic linking header.  With this option, the binary
 	is statically linked and does not refer to dynld.  Without this option
 	(the default), the binary's contents are identical but it is loaded with dynld.
--e
-	Emit an extra ELF-compatible symbol table useful with tools such as
-	nm, gdb, and oprofile. This option makes the binary file considerably larger.
 -Hdarwin
 	Write Apple Mach-O binaries (default when $GOOS is darwin)
 -Hlinux