intro: change byline to "by al." (#6984)

Several people have suggested that the "by Bram" byline is misleading,
it implies that Bram is actively involved with the project. Up to now we
left it as an homage.

Bram agreed that it is misleading, and suggested a mention somewhere
other than the intro.

runtime/doc/intro.txt

@@ -249,8 +249,7 @@ Vi	"the original".  Without further remarks this is the version
 	of Vi that appeared in Sun OS 4.x.  ":version" returns
 	"Version 3.7, 6/7/85".  Sometimes other versions are referred
 	to.  Only runs under Unix.  Source code only available with a
-	license.  More information on Vi can be found through:
-		http://vi-editor.org	[doesn't currently work...]
+	license.
 							*Nvi*
 Nvi	The "New" Vi.  The version of Vi that comes with BSD 4.4 and FreeBSD.
 	Very good compatibility with the original Vi, with a few extensions.

runtime/doc/nvim.txt

@@ -6,6 +6,8 @@
 
 Nvim							   *nvim* *nvim-intro*
 
+Nvim is based on Vim by Bram Moolenaar.
+
 If you are new to Vim see |help.txt|, or type ":Tutor".
 If you already use Vim see |nvim-from-vim| for a quickstart.
 

src/nvim/version.c

@@ -993,7 +993,7 @@ void intro_message(int colon)
   static char *(lines[]) = {
     N_(NVIM_VERSION_LONG),
     "",
-    N_("by Bram Moolenaar et al."),
+    N_("by al."),
     N_("Nvim is open source and freely distributable"),
     N_("https://neovim.io/community"),
     "",