Remove stub flavor of wasm worker library. NFC (#26429)

As far as I can tell there is no way to actually use this library since
libwasm_workers is only ever included when `-sWASM_WORKERS` is used.
Given that it not active/usable I think we should remove it until there
is demand for something like this.

Also, remove the addition of `-fPIC` (that is handled already by
get_base_cflags);
    
Also, remove the addition of `-DNDEBUG` (that is handled already by
DebugLibrary).

Author: sbc100

embuilder.py

@@ -121,7 +121,6 @@
     'libsanitizer_common_rt',
     'libubsan_rt',
     'libwasm_workers-debug',
-    'libwasm_workers-debug-stub',
     'libfetch',
     'libfetch-mt',
     'libwasmfs',

system/lib/wasm_worker/library_wasm_worker_stub.c

@@ -1504,15 +1504,12 @@ def can_use(self):
 class libwasm_workers(DebugLibrary):
   name = 'libwasm_workers'
   includes = ['system/lib/libc']
-
-  def __init__(self, **kwargs):
-    self.is_stub = kwargs.pop('stub')
-    super().__init__(**kwargs)
+  src_dir = 'system/lib/wasm_worker'
+  src_files = ['library_wasm_worker.c', 'wasm_worker_initialize.S']
 
   def get_cflags(self):
-    cflags = super().get_cflags()
+    cflags = super().get_cflags() + ['-sWASM_WORKERS']
     if self.is_debug:
-      cflags += ['-D_DEBUG']
       # library_wasm_worker.c contains an assert that a nonnull parameter
       # is no NULL, which llvm now warns is redundant/tautological.
       cflags += ['-Wno-tautological-pointer-compare']
@@ -1521,45 +1518,12 @@ def get_cflags(self):
       # https://github.com/emscripten-core/emscripten/issues/19331
       cflags += ['-O0']
     else:
-      cflags += ['-DNDEBUG', '-Oz']
-    if settings.MAIN_MODULE:
-      cflags += ['-fPIC']
-    if not self.is_stub:
-      cflags += ['-sWASM_WORKERS']
+      cflags += ['-Oz']
     return cflags
 
-  def get_base_name(self):
-    name = super().get_base_name()
-    if self.is_stub:
-      name += '-stub'
-    return name
-
-  @classmethod
-  def vary_on(cls):
-    return super().vary_on() + ['stub']
-
-  @classmethod
-  def get_default_variation(cls, **kwargs):
-    return super().get_default_variation(stub=not settings.WASM_WORKERS, **kwargs)
-
-  def get_files(self):
-    files = []
-    if self.is_stub:
-      files = [
-        'library_wasm_worker_stub.c',
-      ]
-    else:
-      files = [
-        'library_wasm_worker.c',
-        'wasm_worker_initialize.S',
-      ]
-    return files_in_path(
-        path='system/lib/wasm_worker',
-        filenames=files)
-
   def can_use(self):
     # see src/library_wasm_worker.js
-    return super().can_use() and not settings.SINGLE_FILE and not settings.MAIN_MODULE
+    return super().can_use() and not settings.SINGLE_FILE and not settings.MAIN_MODULE and settings.WASM_WORKERS
 
 
 class libsockets(MuslInternalLibrary, MTLibrary):