Revert "bump maccore to deprecate docs' classic dependency" (#3440)

This reverts commit 95d1968856.

Unfortunately with this commit our build fails with

```
[5:06:58] GEN      XamMac.CFNetwork.xml
[5:06:58] install: ../../../../xamarin-macios/external/macios-binaries/docs/macOS/classic/XamMac.xml: No such file or directory
[5:06:58] install: ../../../../xamarin-macios/external/macios-binaries/docs/macOS/classic/XamMac.CFNetwork.xml: No such file or directory
[5:06:58] make[6]: *** [../../../../xamarin-macios/external/macios-binaries/docs/macOS/classic/XamMac.xml] Error 71
[5:06:58] make[6]: *** Waiting for unfinished jobs....
[5:06:58] make[6]: *** [../../../../xamarin-macios/external/macios-binaries/docs/macOS/classic/XamMac.CFNetwork.xml] Error 71
```

mk/xamarin.mk

@@ -1,5 +1,5 @@
 ifdef ENABLE_XAMARIN
-NEEDED_MACCORE_VERSION := 9de313b2208908e9e687f78764660de168bcba7b
+NEEDED_MACCORE_VERSION := 62c4393c94ed274acbc1edce259a3c22a461f922
 NEEDED_MACCORE_BRANCH := master
 
 MACCORE_DIRECTORY := maccore