piper deps aren't packaged yet, and should be USE conditional anyway

https://bugs.gentoo.org/961974

diff --git a/setup/extensions.json b/setup/extensions.json
index b39ce6d..c105031 100644
--- a/setup/extensions.json
+++ b/setup/extensions.json
@@ -134,14 +134,6 @@
         "error": "!podofo_error",
 		"needs_c++": "17"
     },
-    {
-        "name": "piper",
-        "sources": "calibre/utils/tts/piper.cpp",
-		"needs_c++": "17",
-        "libraries": "!piper_libs",
-        "lib_dirs": "!piper_lib_dirs",
-        "inc_dirs": "!piper_inc_dirs"
-    },
     {
         "name": "html_as_json",
         "sources": "calibre/srv/html_as_json.cpp",
diff --git a/src/calibre/constants.py b/src/calibre/constants.py
index fa4b211459..7b27768953 100644
--- a/src/calibre/constants.py
+++ b/src/calibre/constants.py
@@ -258,7 +258,6 @@ def __init__(self):
             'rcc_backend',
             'icu',
             'speedup',
-            'piper',
             'html_as_json',
             'fast_css_transform',
             'fast_html_entities',
diff --git a/src/calibre/utils/run_tests.py b/src/calibre/utils/run_tests.py
index ffd0f95c04..c80a35f83d 100644
--- a/src/calibre/utils/run_tests.py
+++ b/src/calibre/utils/run_tests.py
@@ -192,6 +192,7 @@ def test_import_of_all_python_modules(self):
             }
         if 'SKIP_SPEECH_TESTS' in os.environ:
             exclude_packages.add('calibre.gui2.tts')
+            exclude_modules.add('calibre.utils.tts.piper')
         if not isbsd:
             exclude_modules.add('calibre.devices.usbms.hal')
         d = os.path.dirname