http: fix v1 protocol tests with apache httpd < 2.4

http: fix v1 protocol tests with apache httpd < 2.4

The apache config used by tests was updated to use the SetEnvIf
directive to set the Git-Protocol header in 19113a26b6 ("http: tell
server that the client understands v1", 2017-10-16).

Setting the Git-Protocol header is restricted to httpd >= 2.4, but
mod_setenvif and the SetEnvIf directive work with lower versions, at
least as far back as 2.0, according to the httpd documentation:

    https://httpd.apache.org/docs/2.0/mod/mod_setenvif.html

Drop the restriction.  Tested with httpd 2.2 and 2.4.

Signed-off-by: Todd Zullinger <tmz@pobox.com>
Acked-by: Brandon Williams <bmwill@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>