Simplify libprintf_long_double. NFC (#26428)

Author: sbc100

tools/system_libs.py

@@ -1494,11 +1494,8 @@ def can_use(self):
 class libprintf_long_double(libc):
   name = 'libprintf_long_double'
   cflags = ['-DEMSCRIPTEN_PRINTF_LONG_DOUBLE']
-
-  def get_files(self):
-    return files_in_path(
-        path='system/lib/libc/musl/src/stdio',
-        filenames=['vfprintf.c'])
+  src_dir = 'system/lib/libc/musl/src/stdio'
+  src_files = ['vfprintf.c']
 
   def can_use(self):
     return super().can_use() and settings.PRINTF_LONG_DOUBLE