Merge bitcoin/bitcoin#23751: build, qt: No need to set inapplicable QPA backend for Android

29e1794 build, qt: No need to set inapplicable QPA backend for Android (Hennadii Stepanov)

Pull request description:

  The current workflow looks weird. At first, the inapplicable `xcb` QPA backend is set in Qt `configure` options. Then the correct `android` QPA backend is forced via the `QT_QPA_PLATFORM` environment variable.

  Using the default QPA backend, which is `android` for Android devices, is just fine.

ACKs for top commit:
  icota:
    re-tACK 29e1794

Tree-SHA512: 08ed7d05209c1bedc1a71de5ea3be5d86b40319a164dceb9191f7a4dfe78f2f951778b90421335e73e71a798a57bdf046aa96876762d338b600037bd7ee27b52

Author: fanquake

depends/packages/qt.mk

@@ -173,7 +173,6 @@ $(package)_config_opts_android += -android-sdk $(ANDROID_SDK)
 $(package)_config_opts_android += -android-ndk $(ANDROID_NDK)
 $(package)_config_opts_android += -android-ndk-platform android-$(ANDROID_API_LEVEL)
 $(package)_config_opts_android += -egl
-$(package)_config_opts_android += -qpa xcb
 $(package)_config_opts_android += -no-dbus
 $(package)_config_opts_android += -opengl es2
 $(package)_config_opts_android += -qt-freetype

src/qt/android/src/org/bitcoincore/qt/BitcoinQtActivity.java

@@ -18,12 +18,6 @@ public void onCreate(Bundle savedInstanceState)
             bitcoinDir.mkdir();
         }
 
-        try {
-            Os.setenv("QT_QPA_PLATFORM", "android", true);
-        } catch (ErrnoException e) {
-            e.printStackTrace();
-        }
-
         super.onCreate(savedInstanceState);
     }
 }