[libc][NFC] Remove cpp20 requirement for arpa/inet test (llvm#163983)

Address
llvm#162651 (comment).

Author: c8ef

libc/test/src/arpa/inet/CMakeLists.txt

@@ -6,8 +6,6 @@ add_libc_unittest(
     libc_arpa_inet_unittests
   SRCS
     htonl_test.cpp
-  CXX_STANDARD
-    20
   DEPENDS
     libc.src.arpa.inet.htonl
     libc.src.arpa.inet.ntohl
@@ -19,8 +17,6 @@ add_libc_unittest(
     libc_arpa_inet_unittests
   SRCS
     htons_test.cpp
-  CXX_STANDARD
-    20
   DEPENDS
     libc.src.arpa.inet.htons
     libc.src.arpa.inet.ntohs
@@ -32,8 +28,6 @@ add_libc_unittest(
     libc_arpa_inet_unittests
   SRCS
     ntohl_test.cpp
-  CXX_STANDARD
-    20
   DEPENDS
     libc.src.arpa.inet.htonl
     libc.src.arpa.inet.ntohl
@@ -45,8 +39,6 @@ add_libc_unittest(
     libc_arpa_inet_unittests
   SRCS
     ntohs_test.cpp
-  CXX_STANDARD
-    20
   DEPENDS
     libc.src.arpa.inet.htons
     libc.src.arpa.inet.ntohs