INSTALL: remove discussion of SHA-1 backends

The claim that OpenSSL is the default SHA-1 backend hasn't been true
since e6b07da (Makefile: make DC_SHA1 the default, 2017-03-17),
but more importantly tweaking the SHA-1 backend isn't something that's
common enough to warrant discussing in the INSTALL document, so let's
remove this paragraph.

This discussion was originally added in c538d2d (Add some
installation notes in INSTALL, 2005-06-17) when tweaking the default
backend was more common. The current wording was added in
5beb577 (INSTALL: Describe dependency knobs from Makefile,
2009-09-10).

Signed-off-by: Ævar Arnfjörð Bjarmason <[email protected]>
Signed-off-by: Taylor Blau <[email protected]>

Author: avar

INSTALL

@@ -133,10 +133,6 @@ Issues of note:
 	  you are using libcurl older than 7.34.0.  Otherwise you can use
 	  NO_OPENSSL without losing git-imap-send.
 
-	  By default, git uses OpenSSL for SHA1 but it will use its own
-	  library (inspired by Mozilla's) with either NO_OPENSSL or
-	  BLK_SHA1.
-
 	- "libcurl" library is used for fetching and pushing
 	  repositories over http:// or https://, as well as by
 	  git-imap-send if the curl version is >= 7.34.0. If you do