runtime: delete redundant code in the page allocator

The page allocator's scavenge index has sysGrow called on it twice,
once in pageAlloc.grow, and once in pageAlloc.sysGrow on 64-bit
platforms. Calling it twice is OK since sysGrow is idempotent,
but it's also wasteful. This change removes the call
in pageAlloc.sysGrow.

Change-Id: I5b955b6e2beed5c2b8305ab82b76718ea305792c
Reviewed-on: https://go-review.googlesource.com/c/go/+/707735
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Michael Knyszek <[email protected]>
Reviewed-by: Carlos Amedee <[email protected]>

Author: tony

src/runtime/mpagealloc_64bit.go

@@ -180,9 +180,6 @@ func (p *pageAlloc) sysGrow(base, limit uintptr) {
 		sysUsed(unsafe.Pointer(need.base.addr()), need.size(), need.size())
 		p.summaryMappedReady += need.size()
 	}
-
-	// Update the scavenge index.
-	p.summaryMappedReady += p.scav.index.sysGrow(base, limit, p.sysStat)
 }
 
 // sysGrow increases the index's backing store in response to a heap growth.