Drop mentions of core.js in options (#2263)

cmd/runtime_options.go

@@ -60,9 +60,9 @@ func runtimeOptionFlagSet(includeSysEnv bool) *pflag.FlagSet {
 	flags.Bool("include-system-env-vars", includeSysEnv, "pass the real system environment variables to the runtime")
 	flags.String("compatibility-mode", "extended",
 		`JavaScript compiler compatibility mode, "extended" or "base"
-base: pure Golang JS VM supporting ES5.1+
-extended: base + Babel with ES2015 preset + core.js v2,
-          slower and memory consuming but with greater JS support
+base: pure goja - Golang JS VM supporting ES5.1+
+extended: base + Babel with parts of ES2015 preset
+		  slower to compile in case the script uses syntax unsupported by base
 `)
 	flags.StringArrayP("env", "e", nil, "add/override environment variable with `VAR=value`")
 	flags.Bool("no-thresholds", false, "don't run thresholds")

lib/runtime_options.go

@@ -33,7 +33,7 @@ import (
 type CompatibilityMode uint8
 
 const (
-	// CompatibilityModeExtended achieves ES6+ compatibility with Babel and core.js
+	// CompatibilityModeExtended achieves ES6+ compatibility with Babel
 	CompatibilityModeExtended CompatibilityMode = iota + 1
 	// CompatibilityModeBase is standard goja ES5.1+
 	CompatibilityModeBase
@@ -44,7 +44,7 @@ type RuntimeOptions struct {
 	// Whether to pass the actual system environment variables to the JS runtime
 	IncludeSystemEnvVars null.Bool `json:"includeSystemEnvVars"`
 
-	// JS compatibility mode: "extended" (Goja+Babel+core.js) or "base" (plain Goja)
+	// JS compatibility mode: "extended" (Goja+Babel) or "base" (plain Goja)
 	//
 	// TODO: when we resolve https://github.com/k6io/k6/issues/883, we probably
 	// should use the CompatibilityMode type directly... but by then, we'd need to have