check remote-servers list correctness

check remote-servers list correctness

`check.c` only checks if `remote-servers`, `primaries`, etc. are not
duplicated inside the configuration file, but does not check the
correctness of its definition. This commit fixes this by calling
`validate_remotes()` for each `remote-servers` (and other aliases),
which validates the correctness of the definition itself (this is the
same call done to validate other cases like `also-notify`, etc.).

(cherry picked from commit 1a732b6b8ecc89232724d80adba84350976ae2ca)