Remove lua.Lock

Exposing locking primitives to lua plugins is tricky and may lead to
deadlocks. Instead, if possible, it's better to ensure all the needed
synchonization in micro itself, without leaving this burden to lua code.

Since we've added micro.After() timer API and removed exposing Go timers
directly to lua, now we (probably?) have no cases of lua code possibly
running asynchronously without micro controlling when it is running. So
now we can remove lua.Lock.

This means breaking compatibility, but, until recently lua.Lock wasn't
workable at all (see zyedidia#2945), which suggests that it has never been
really used by anyone. So it should be safe to remove it.

cmd/micro/initlua.go

@@ -55,7 +55,6 @@ func luaImportMicro() *lua.LTable {
 	ulua.L.SetField(pkg, "Tabs", luar.New(ulua.L, func() *action.TabList {
 		return action.Tabs
 	}))
-	ulua.L.SetField(pkg, "Lock", luar.New(ulua.L, &ulua.Lock))
 	ulua.L.SetField(pkg, "After", luar.New(ulua.L, func(t time.Duration, f func()) {
 		time.AfterFunc(t, func() {
 			timerChan <- f

cmd/micro/micro.go

@@ -23,7 +23,6 @@ import (
 	"github.com/zyedidia/micro/v2/internal/buffer"
 	"github.com/zyedidia/micro/v2/internal/clipboard"
 	"github.com/zyedidia/micro/v2/internal/config"
-	ulua "github.com/zyedidia/micro/v2/internal/lua"
 	"github.com/zyedidia/micro/v2/internal/screen"
 	"github.com/zyedidia/micro/v2/internal/shell"
 	"github.com/zyedidia/micro/v2/internal/util"
@@ -418,15 +417,11 @@ func DoEvent() {
 	select {
 	case f := <-shell.Jobs:
 		// If a new job has finished while running in the background we should execute the callback
-		ulua.Lock.Lock()
 		f.Function(f.Output, f.Args)
-		ulua.Lock.Unlock()
 	case <-config.Autosave:
-		ulua.Lock.Lock()
 		for _, b := range buffer.OpenBuffers {
 			b.Save()
 		}
-		ulua.Lock.Unlock()
 	case <-shell.CloseTerms:
 	case event = <-screen.Events:
 	case <-screen.DrawChan():
@@ -478,12 +473,10 @@ func DoEvent() {
 		return
 	}
 
-	ulua.Lock.Lock()
 	_, resize := event.(*tcell.EventResize)
 	if action.InfoBar.HasPrompt && !resize {
 		action.InfoBar.HandleEvent(event)
 	} else {
 		action.Tabs.HandleEvent(event)
 	}
-	ulua.Lock.Unlock()
 }

internal/lua/lua.go

@@ -17,7 +17,6 @@ import (
 	"regexp"
 	"runtime"
 	"strings"
-	"sync"
 	"time"
 	"unicode/utf8"
 
@@ -27,7 +26,6 @@ import (
 )
 
 var L *lua.LState
-var Lock sync.Mutex
 
 // LoadFile loads a lua file
 func LoadFile(module string, file string, data []byte) error {