Revert "guard" in Tr function

otherwise the unit-tests will fail:

=== RUN   TestBoardOptions
--- FAIL: TestBoardOptions (0.00s)
panic: i18n.Tr called before i18n.Init() [recovered]
	panic: i18n.Tr called before i18n.Init()

goroutine 9 [running]:
testing.tRunner.func1.2(0xc56e00, 0xeaee20)
	/opt/hostedtoolcache/go/1.16.7/x64/src/testing/testing.go:1143 +0x332
testing.tRunner.func1(0xc0002a2f00)
	/opt/hostedtoolcache/go/1.16.7/x64/src/testing/testing.go:1146 +0x4b6
panic(0xc56e00, 0xeaee20)
	/opt/hostedtoolcache/go/1.16.7/x64/src/runtime/panic.go:965 +0x1b9
github.com/arduino/arduino-cli/i18n.Tr(0xdceacd, 0x28, 0x0, 0x0, 0x0, 0x0, 0x1)
	/home/runner/work/arduino-cli/arduino-cli/i18n/i18n.go:54 +0xd9
github.com/arduino/arduino-cli/arduino/cores.(*Board).GetBuildProperties(0x13bf060, 0xc0003b6150, 0xc000339400, 0x0, 0x0)
	/home/runner/work/arduino-cli/arduino-cli/arduino/cores/board.go:109 +0x69d
github.com/arduino/arduino-cli/arduino/cores.(*Board).GeneratePropertiesForConfiguration(0x13bf060, 0xdb5f54, 0xe, 0xc000309ef0, 0xc911e0, 0xc0003b6000)
	/home/runner/work/arduino-cli/arduino-cli/arduino/cores/board.go:141 +0x28f
github.com/arduino/arduino-cli/arduino/cores.TestBoardOptions(0xc0002a2f00)
	/home/runner/work/arduino-cli/arduino-cli/arduino/cores/board_test.go:298 +0x4bd
testing.tRunner(0xc0002a2f00, 0xe052a8)
	/opt/hostedtoolcache/go/1.16.7/x64/src/testing/testing.go:1193 +0xef
created by testing.(*T).Run
	/opt/hostedtoolcache/go/1.16.7/x64/src/testing/testing.go:1238 +0x2b3
FAIL	github.com/arduino/arduino-cli/arduino/cores	0.021s
=== RUN   TestIndexParsing
--- FAIL: TestIndexParsing (0.00s)
panic: i18n.Tr called before i18n.Init() [recovered]
	panic: i18n.Tr called before i18n.Init()

Author: cmaglie

i18n/i18n.go

@@ -15,15 +15,11 @@
 
 package i18n
 
-var initialized = false
-
 // Init initializes the i18n module, setting the locale according to this order of preference:
 // 1. Locale specified via the function call
 // 2. OS Locale
 // 3. en (default)
 func Init(configLocale ...string) {
-	defer func() { initialized = true }()
-
 	initRiceBox()
 	locales := supportedLocales()
 	if len(configLocale) > 1 {
@@ -50,8 +46,5 @@ func Init(configLocale ...string) {
 // Tr returns msg translated to the selected locale
 // the msg argument must be a literal string
 func Tr(msg string, args ...interface{}) string {
-	if !initialized {
-		panic("i18n.Tr called before i18n.Init()")
-	}
 	return po.Get(msg, args...)
 }