Don't initialize plugins in buffer test and rtfiles test

Adding InitPlugins() to tests has caused noisy error logs when running
the buffer_test.go test (although the test result is still PASS):

2024/03/23 15:14:30 Plugin does not exist: autoclose at autoclose : &{autoclose autoclose <nil> [runtime/plugins/autoclose/autoclose.lua] false true}
2024/03/23 15:14:30 Plugin does not exist: comment at comment : &{comment comment <nil> [runtime/plugins/comment/comment.lua] false true}
2024/03/23 15:14:30 Plugin does not exist: diff at diff : &{diff diff <nil> [runtime/plugins/diff/diff.lua] false true}
2024/03/23 15:14:30 Plugin does not exist: ftoptions at ftoptions : &{ftoptions ftoptions <nil> [runtime/plugins/ftoptions/ftoptions.lua] false true}
...

These errors are caused simply by the fact that plugins are initialized
but not loaded. Adding config.LoadAllPlugins() to buffer_test.go "fixes"
this problem.

However, at the moment it doesn't seem a good idea to load plugins in
buffer_test.go, since buffer_test.go doesn't properly initialize Lua. It
only does ulua.L = lua.NewState() but doesn't do the other stuff that
init() in cmd/micro/initlua.go does. As a result, plugins will not be
able to do anything correctly.

So in order to initialize Lua correctly we need to be inside cmd/micro/,
so we cannot do it in buffer_test.go or any other tests except
micro_test.go.

internal/buffer/buffer_test.go

@@ -21,7 +21,6 @@ type operation struct {
 func init() {
 	ulua.L = lua.NewState()
 	config.InitRuntimeFiles()
-	config.InitPlugins()
 	config.InitGlobalSettings()
 	config.GlobalSettings["backup"] = false
 	config.GlobalSettings["fastdirty"] = true

internal/config/rtfiles_test.go

@@ -8,7 +8,6 @@ import (
 
 func init() {
 	InitRuntimeFiles()
-	InitPlugins()
 }
 
 func TestAddFile(t *testing.T) {