Remove advanced setting `ignoreScriptInjectFilters`

This advanced setting is not really needed, as the
same can be accomplished with a broad exception
filter such as `#@#+js()`.

Related feedback:
- f5b453fae3 (commitcomment-49499082)

src/js/background.js

@@ -63,7 +63,6 @@ const µBlock = (( ) => { // jshint ignore:line
         extensionUpdateForceReload: false,
         filterAuthorMode: false,
         filterOnHeaders: false,
-        ignoreScriptInjectFilters: false,
         loggerPopupType: 'popup',
         manualUpdateAssetFetchPeriod: 500,
         popupFontSize: 'unset',

src/js/scriptlet-filtering.js

@@ -302,7 +302,6 @@
 
     api.retrieve = function(request) {
         if ( scriptletDB.size === 0 ) { return; }
-        if ( µb.hiddenSettings.ignoreScriptInjectFilters ) { return; }
 
         const reng = µb.redirectEngine;
         if ( !reng ) { return; }

src/js/static-ext-filtering.js

@@ -180,12 +180,11 @@
                 if ( iHn !== undefined ) {
                     do {
                         const strId = this.hostnameSlots[iHn+0];
-                        if ( this.strSlots[strId >>> this.nBits] === value ) {
+                        const str = this.strSlots[strId >>> this.nBits];
                         if ( (strId & exceptionBit) !== 0 ) {
-                                return false;
-                            }
-                            found = true;
+                            if ( str === value || str === '' ) { return false; }
                         }
+                        if ( str === value ) { found = true; }
                         iHn = this.hostnameSlots[iHn+1];
                     } while ( iHn !== 0 );
                 }