runtime: remove GODEBUG=scavenge mode

Change-Id: Ic4c7b5086303c7faa49f4cbf6738e66d5de35c7e
Reviewed-on: https://go-review.googlesource.com/c/go/+/282012
Trust: Michael Pratt <[email protected]>
Run-TryBot: Michael Pratt <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Austin Clements <[email protected]>

Author: WangLeonard

src/runtime/extern.go

@@ -110,8 +110,6 @@ It is a comma-separated list of name=val pairs setting these named variables:
 	with a trivial allocator that obtains memory from the operating system and
 	never reclaims any memory.
 
-	scavenge: scavenge=1 enables debugging mode of heap scavenger.
-
 	scavtrace: setting scavtrace=1 causes the runtime to emit a single line to standard
 	error, roughly once per GC cycle, summarizing the amount of work done by the
 	scavenger as well as the total amount of memory returned to the operating system

src/runtime/runtime1.go

@@ -310,7 +310,6 @@ var debug struct {
 	gctrace            int32
 	invalidptr         int32
 	madvdontneed       int32 // for Linux; issue 28466
-	scavenge           int32
 	scavtrace          int32
 	scheddetail        int32
 	schedtrace         int32
@@ -339,7 +338,6 @@ var dbgvars = []dbgVar{
 	{"invalidptr", &debug.invalidptr},
 	{"madvdontneed", &debug.madvdontneed},
 	{"sbrk", &debug.sbrk},
-	{"scavenge", &debug.scavenge},
 	{"scavtrace", &debug.scavtrace},
 	{"scheddetail", &debug.scheddetail},
 	{"schedtrace", &debug.schedtrace},