Documentation: remove duplicated words

Remove many duplicated words under Documentation/ and do other small
cleanups.

Examples:
        "and and" --> "and"
        "in in" --> "in"
        "the the" --> "the"
        "the the" --> "to the"
        ...

Signed-off-by: Paolo Ornati <ornati@fastwebnet.it>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
diff --git a/Documentation/keys.txt b/Documentation/keys.txt
index 693ef0c..3da586b 100644
--- a/Documentation/keys.txt
+++ b/Documentation/keys.txt
@@ -671,7 +671,7 @@
 
      Note that this setting is inherited across fork/exec.
 
-     [1] The default default is: the thread keyring if there is one, otherwise
+     [1] The default is: the thread keyring if there is one, otherwise
      the process keyring if there is one, otherwise the session keyring if
      there is one, otherwise the user default session keyring.