internal/goexperiment: actually delete goroutineleakprofile experiment

CL 774621 deleted the generated _on, _off files of the
goroutineleakprofile experiment and all uses of it, but did not
delete the definition of the flag itself, leaving
internal/goexperiment not "go generate"-clean. This CL actually
deletes the flag.

Updates #74609.

Change-Id: I1e3f49eeaf5691fc70e4dc34aae364de95f79571
Reviewed-on: https://go-review.googlesource.com/c/go/+/775621
TryBot-Bypass: Cherry Mui <cherryyz@google.com>
Auto-Submit: Austin Clements <austin@google.com>
Reviewed-by: Austin Clements <austin@google.com>

src/internal/buildcfg/exp.go

@@ -84,7 +84,6 @@ func ParseGOEXPERIMENT(goos, goarch, goexp string) (*ExperimentFlags, error) {
 		Dwarf5:               dwarf5Supported,
 		RandomizedHeapBase64: true,
 		GreenTeaGC:           true,
-		GoroutineLeakProfile: true,
 	}
 	flags := &ExperimentFlags{
 		Flags:    baseline,

src/internal/goexperiment/flags.go

@@ -122,9 +122,6 @@ type Flags struct {
 	// SizeSpecializedMalloc enables malloc implementations that are specialized per size class.
 	SizeSpecializedMalloc bool
 
-	// GoroutineLeakProfile enables the collection of goroutine leak profiles.
-	GoroutineLeakProfile bool
-
 	// SIMD enables the simd package and the compiler's handling
 	// of SIMD intrinsics.
 	SIMD bool