Remove `scrollback` feature.

Squashed commit of the following:

commit aab2886e03e4a239aca6e013454864734b669f76
Author: Mateja <mail@matejamaric.com>
Date:   Sun Apr 11 16:10:22 2021 +0200

    Revert "Applied first `scrollback` patch."

    This reverts commit e2a49699774c0256f6c745c55f42c7c56a5e0d95.

commit 16f52eb7d91426aec2f92dd46d90031402567889
Author: Mateja <mail@matejamaric.com>
Date:   Sun Apr 11 16:08:30 2021 +0200

    Revert "Applied second `scrollback` patch."

    This reverts commit 09f652d8aff93ba8b7e96d07a58c1aa520f44a2f.

commit 9b55f3b7607c44d1c26353d3e9d6d23d59758195
Author: Mateja <mail@matejamaric.com>
Date:   Sun Apr 11 16:08:18 2021 +0200

    Revert "Applied third `scrollback` patch."

    This reverts commit c2131a689c5b83d2f5015f5afdce5ab3bc58e734.

commit 0a2f1c12ae3e9134df6b92f1a9443369f8fac591
Author: Mateja <mail@matejamaric.com>
Date:   Sun Apr 11 16:06:48 2021 +0200

    Revert "Add `scrollback` to README."

    This reverts commit 1c354fe11695ffa5d00bcc86ecb84c7edb1fd7b6.

1 files changed, 0 insertions, 3 deletions

diff --git a/st.h b/st.h
index b41e6c0..315fb02 100644
--- a/st.h
+++ b/st.h
@@ -83,8 +83,6 @@ void redraw(void);
 void draw(void);
 
 void externalpipe(const Arg *);
-void kscrolldown(const Arg *);
-void kscrollup(const Arg *);
 void newterm(const Arg *);
 void printscreen(const Arg *);
 void printsel(const Arg *);
@@ -92,7 +90,6 @@ void sendbreak(const Arg *);
 void toggleprinter(const Arg *);
 
 int tattrset(int);
-int tisaltscr(void);
 void tnew(int, int);
 void tresize(int, int);
 void tsetdirtattr(int);