Removed sdbm entries from doc

Merged: https://github.com/ruby/ruby/pull/3234

LEGAL

@@ -446,7 +446,7 @@ mentioned below.
 
   >>>
     A C-program for MT19937, with initialization improved 2002/2/10.::
-    Coded by Takuji Nishimura and Makoto Matsumoto.  
+    Coded by Takuji Nishimura and Makoto Matsumoto.
     This is a faster version by taking Shawn Cokus's optimization,
     Matthe Bellew's simplification, Isaku Wada's real version.
 
@@ -553,8 +553,6 @@ mentioned below.
 [ext/date/date_strftime.c]
 [ext/digest/sha1/sha1.c]
 [ext/digest/sha1/sha1.h]
-[ext/sdbm/_sdbm.c]
-[ext/sdbm/sdbm.h]
 
   These files are all under public domain.
 

doc/maintainers.rdoc

@@ -328,10 +328,6 @@ Zachary Scott (zzak)
   TAKAO Kouji (kouji)
   https://github.com/ruby/readline-ext
   http:://rubygems.org/gems/readline-ext
-[ext/sdbm]
-  Yukihiro Matsumoto (matz)
-  https://github.com/ruby/sdbm
-  https://rubygems.org/gems/sdbm
 [ext/stringio]
   Nobuyuki Nakada (nobu)
   https://github.com/ruby/stringio

doc/standard_library.rdoc

@@ -102,7 +102,6 @@ JSON:: Implements Javascript Object Notation for Ruby
 OpenSSL:: Provides SSL, TLS and general purpose cryptography for Ruby
 Psych:: A YAML parser and emitter for Ruby
 Readline:: Provides an interface for GNU Readline and Edit Line (libedit)
-SDBM:: Provides a simple file-based key-value store with String keys and values
 StringIO:: Pseudo I/O on String objects
 StringScanner:: Provides lexical scanning operations on a String
 Zlib:: Ruby interface for the zlib compression/decompression library