Use default symbol_level

Increases android gold builds by 0.25mb and provides better symbols
when symbolizing crashes.

b/389688740

cobalt/build/gn.py

@@ -47,19 +47,15 @@ def get_build_args(build_args_path):
 
 _BUILD_TYPES = {
     'debug': {
-        'symbol_level': 2,
         'is_debug': 'true',
     },
     'devel': {
-        'symbol_level': 1,
         'is_debug': 'false',
     },
     'qa': {
-        'symbol_level': 1,
         'is_official_build': 'true'
     },
     'gold': {
-        'symbol_level': 0,
         'is_official_build': 'true',
         'cobalt_is_release_build': 'true'
     }