Replace browser conditions by preprocessed conditions

The extension used to rely on the isFirefox method to check whether the
browser is Firefox or Chromium-based. This CL removes this function and
replaces the conditions based in this function by conditions which are
pre-processed at compile time.

Change-Id: Id7280e6c8fb3dfd3fabbc05339ef3791822aa6ac
diff --git a/src/options/optionsPage.json5 b/src/options/optionsPage.json5
index 24bafdd..a06819a 100644
--- a/src/options/optionsPage.json5
+++ b/src/options/optionsPage.json5
@@ -36,7 +36,9 @@
         {codename: 'increasecontrast'},
         {codename: 'stickysidebarheaders'},
         {codename: 'ccforcehidedrawer'},
-        {codename: 'ccdragndropfix', customHTML: '<div id="dragndrop-wrapper" class="option" hidden><input type="checkbox" id="ccdragndropfix"> <label for="ccdragndropfix" data-i18n="ccdragndropfix"></label></div>'},
+        // #!if ['chromium', 'chromium_mv3'].includes(browser_target)
+        {codename: 'ccdragndropfix'},
+        // #!endif
         {codename: 'enhancedannouncementsdot'},
         {codename: 'repositionexpandthread', experimental: true},
         {codename: 'imagemaxheight'},