Remove unused STATICLIB_ENDINGS. NFC (#23463)

Author: sbc100

tools/shared.py

@@ -825,7 +825,6 @@ class OFormat(Enum):
 # Windows .dll suffix is not included in this list, since those are never
 # linked to directly on the command line.
 DYNAMICLIB_ENDINGS = ['.dylib', '.so']
-STATICLIB_ENDINGS = ['.a']
 
 run_via_emxx = False