Revert "proc: Fix parsing of 'BuildVersion' on Go tip"

This reverts commit ad5097a8.
runtime/internal/sys.BuildVersion was not used in any official
release.

proc/proc.go

@@ -705,13 +705,10 @@ func (dbp *Process) execPtraceFunc(fn func()) {
 }
 
 func (dbp *Process) getGoInformation() (ver GoVersion, isextld bool, err error) {
-	vv, err := dbp.EvalPackageVariable("runtime/internal/sys.BuildVersion")
+	vv, err := dbp.EvalPackageVariable("runtime.buildVersion")
 	if err != nil {
-		vv, err = dbp.EvalPackageVariable("runtime.buildVersion")
-		if err != nil {
-			err = fmt.Errorf("Could not determine version number: %v\n", err)
-			return
-		}
+		err = fmt.Errorf("Could not determine version number: %v\n", err)
+		return
 	}
 
 	ver, ok := parseVersionString(constant.StringVal(vv.Value))