Revert "net: ipv6: Add IPv6 support to the ping socket."

This reverts commit 4b79296446a6afc2a99e63b703da349dc729a9b7.
Revert "net: ipv6: add missing lock in ping_v6_sendmsg"

This reverts commit 0ab17b82a0cee73cd6bc552e53779d5a6aa02f71.
Revert "net: ipv6: fix wrong ping_v6_sendmsg return value"

This reverts commit 0f9ec6cb0e23c78b329e2dcdfd9f0704f6ebaf19.