fix constants

Author: younesbelkada

gguf-py/gguf/constants.py

@@ -172,7 +172,6 @@ class SSM:
         TIME_STEP_RANK = "{arch}.ssm.time_step_rank"
         GROUP_COUNT    = "{arch}.ssm.group_count"
         DT_B_C_RMS     = "{arch}.ssm.dt_b_c_rms"
-        HEAD_DIM       = "{arch}.ssm.head_dim"
 
     class WKV:
         HEAD_SIZE = "{arch}.wkv.head_size"