Don't use 'dialog=no' or 'modal' for preferences window

Since at least 2009, for reasons unclear, we've used `dialog=no` when
`instantApply` is true (macOS/Linux) and `modal` (with implicit
`dialog=yes`) when false (Windows). `dialog=no` doesn't seem to have an
effect on macOS, and `modal` doesn't seem to have an effect on Windows
(at least with `openDialog()`), but on Linux `dialog=no` allows the
dialog to be resized, which it shouldn't be, and causes problems with a
tiling window manager. This change switches to the implicit `dialog=yes`
on all platforms. (On Linux, this also centers the dialog on the screen,
keeps it in front of other windows, and does a weird opening animation.)

https://forums.zotero.org/discussion/82050/zotero-preferences-window-issue-with-tiling-window-managers

chrome/content/zotero/xpcom/utilities_internal.js

@@ -1744,8 +1744,7 @@ Zotero.Utilities.Internal = {
 			let args = [
 				'chrome://zotero/content/preferences/preferences.xul',
 				'zotero-prefs',
-				'chrome,titlebar,toolbar,centerscreen,'
-					+ Zotero.Prefs.get('browser.preferences.instantApply', true) ? 'dialog=no' : 'modal',
+				'chrome,titlebar,toolbar,centerscreen',
 				io
 			];