[api-minor] Remove the disableCombineTextItems option

*Please note:* This parameter has never been used within the PDF.js library/viewer itself, and it was only ever added for backwards compatibility reasons.

This parameter was added in PR 7475, over six years ago, to try and optionally maintain the previous *default* text-extraction behaviour.
However as part of the general text-extraction improvements in PR 13257, almost two years ago, the `disableCombineTextItems` functionality was accidentally "broken" in various ways. Note how the only (very basic) unit-test was updated in a way that doesn't really make sense, since generally speaking you'd expect that using the option should result in *more* (or at least the same number of) text-items. Furthermore there's also the recent issue 16209, where the option causes almost all textContent to be concatenated together.

Hence this patch proposes that we simply remove the `disableCombineTextItems` option since it's essentially unused/untested functionality, as evident from the fact that it took almost two years for someone to notice that it's broken.

src/core/worker.js

@@ -741,7 +741,7 @@ class WorkerMessageHandler {
     });
 
     handler.on("GetTextContent", function (data, sink) {
-      const pageIndex = data.pageIndex;
+      const { pageIndex, includeMarkedContent } = data;
 
       pdfManager.getPage(pageIndex).then(function (page) {
         const task = new WorkerTask("GetTextContent: page " + pageIndex);
@@ -755,8 +755,7 @@ class WorkerMessageHandler {
             handler,
             task,
             sink,
-            includeMarkedContent: data.includeMarkedContent,
-            combineTextItems: data.combineTextItems,
+            includeMarkedContent,
           })
           .then(
             function () {