[Android] Enable CoverBrowser (#3264)

I was reminded by @KenMaltby that this is disabled on Android.

https://www.mobileread.com/forums/showthread.php?p=3586162#post3586162

plugins/coverbrowser.koplugin/main.lua

@@ -1,4 +1,3 @@
-local Device = require("device")
 local InputContainer = require("ui/widget/container/inputcontainer")
 local UIManager = require("ui/uimanager")
 local logger = require("logger")
@@ -38,12 +37,7 @@ local CoverBrowser = InputContainer:new{}
 
 function CoverBrowser:init()
     self.full_featured = true
-    -- As we don't know how to run and kill subprocesses on Android (for
-    -- background info extraction), this plugin is very limited on Android,
-    -- and will provide only a menu for managing a few core settings.
-    if Device.isAndroid() then
-        self.full_featured = false
-    end
+    -- Set to false to provide a fallback option with only a menu for managing a few core settings.
 
     self.ui.menu:registerToMainMenu(self)
 

plugins/coverbrowser.koplugin/xutil.lua

@@ -1,5 +1,4 @@
 local ffi = require("ffi")
-local util = require("ffi/util")
 local C = ffi.C
 
 -- Utilities functions needed by this plugin, but that may be added to
@@ -9,24 +8,19 @@ local xutil = {}
 
 -- Sub-process management (may be put into base/ffi/util.lua)
 function xutil.runInSubProcess(func)
-    if util.isAndroid() then
-        -- not sure how to do that on android
-        return nil
-    else
-        local pid = C.fork()
-        if pid == 0 then -- child process
-            -- Just run the provided lua code object in this new process,
-            -- and exit immediatly (so we do not release drivers and
-            -- resources still used by parent process)
-            func()
-            os.exit(0)
-        end
-        -- parent/main process, return pid of child
-        if pid == -1 then -- On failure, -1 is returned in the parent
-            return false
-        end
-        return pid
+    local pid = C.fork()
+    if pid == 0 then -- child process
+        -- Just run the provided lua code object in this new process,
+        -- and exit immediatly (so we do not release drivers and
+        -- resources still used by parent process)
+        func()
+        os.exit(0)
     end
+    -- parent/main process, return pid of child
+    if pid == -1 then -- On failure, -1 is returned in the parent
+        return false
+    end
+    return pid
 end
 
 function xutil.isSubProcessDone(pid)