prompt.c: remove git_getpass() nobody uses

This was whittled down to a compatibility wrapper around the more
flexible git_prompt() in 1cb0134f (refactor git_getpass into generic
prompt function, 2011-12-10), waiting for the final callers to go
away.  That happened in 791643a8 (imap-send: use git-credential,
2014-04-28) when imap-send learned to use the credential interface.

Reviewed-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

prompt.c

@@ -73,8 +73,3 @@ char *git_prompt(const char *prompt, int flags)
 	}
 	return r;
 }
-
-char *git_getpass(const char *prompt)
-{
-	return git_prompt(prompt, PROMPT_ASKPASS);
-}

prompt.h

@@ -5,6 +5,5 @@
 #define PROMPT_ECHO    (1<<1)
 
 char *git_prompt(const char *prompt, int flags);
-char *git_getpass(const char *prompt);
 
 #endif /* PROMPT_H */