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/prio_tree.txt b/Documentation/prio_tree.txt
index 2fbb0c4..3aa68f9 100644
--- a/Documentation/prio_tree.txt
+++ b/Documentation/prio_tree.txt
@@ -88,7 +88,7 @@
 heap-and-size indexed overflow-sub-trees using prio_tree->index_bits.
 Instead the overflow sub-trees are indexed using full BITS_PER_LONG bits
 of size_index. This may lead to skewed sub-trees because most of the
-higher significant bits of the size_index are likely to be be 0 (zero). In
+higher significant bits of the size_index are likely to be 0 (zero). In
 the example above, all 3 overflow-sub-trees are skewed. This may marginally
 affect the performance. However, processes rarely map many vmas with the
 same start_vm_pgoff but different end_vm_pgoffs. Therefore, we normally