[GCU]Fix rdma check failure (#2824)

What I did
if substring.isdigit() and re.match(r'^\d{8}$', substring): In this version check, it only applies to this pattern: 20220531.XXX. It will fail the master and other build check. For example, master.261851-010dc3957 is a master build_version string. It will fail version validation and return failure.

My thought to remove the check is that GCU is only supported in 202205 and later. Either branch_version >= "20201200" or branch_version >= "20181100" is already satisfied.

How I did it
Remove redundant check in GCU RDMA validator

How to verify it
Unit test

generic_config_updater/field_operation_validators.py

@@ -3,24 +3,8 @@
 
 def rdma_config_update_validator():
     version_info = device_info.get_sonic_version_info()
-    build_version = version_info.get('build_version')
     asic_type = version_info.get('asic_type')
 
     if (asic_type != 'mellanox' and asic_type != 'broadcom' and asic_type != 'cisco-8000'):
         return False
-
-    version_substrings = build_version.split('.')
-    branch_version = None
-
-    for substring in version_substrings:
-        if substring.isdigit() and re.match(r'^\d{8}$', substring):
-            branch_version = substring
-            break
-
-    if branch_version is None:
-        return False
-
-    if asic_type == 'cisco-8000':
-        return branch_version >= "20201200"
-    else:
-        return branch_version >= "20181100"
+    return True