Remove duplicate words in comments.

Found these with grep -r "for for ".

src/backend/access/spgist/spgdoinsert.c

@@ -818,7 +818,7 @@ doPickSplit(Relation index, SpGistState *state,
 
 	/*
 	 * We may not actually insert new tuple because another picksplit may be
-	 * necessary due to too large value, but we will try to to allocate enough
+	 * necessary due to too large value, but we will try to allocate enough
 	 * space to include it; and in any case it has to be included in the input
 	 * for the picksplit function.  So don't increment nToInsert yet.
 	 */

src/backend/storage/ipc/standby.c

@@ -283,7 +283,7 @@ ResolveRecoveryConflictWithTablespace(Oid tsid)
 	VirtualTransactionId *temp_file_users;
 
 	/*
-	 * Standby users may be currently using this tablespace for for their
+	 * Standby users may be currently using this tablespace for their
 	 * temporary files. We only care about current users because
 	 * temp_tablespace parameter will just ignore tablespaces that no longer
 	 * exist.

src/backend/tcop/postgres.c

@@ -3021,7 +3021,7 @@ check_stack_depth(void)
 	long		stack_depth;
 
 	/*
-	 * Compute distance from reference point to to my local variables
+	 * Compute distance from reference point to my local variables
 	 */
 	stack_depth = (long) (stack_base_ptr - &stack_top_loc);
 

src/backend/utils/adt/numeric.c

@@ -3503,7 +3503,7 @@ get_str_from_var(NumericVar *var, int dscale)
 	/*
 	 * Allocate space for the result.
 	 *
-	 * i is set to to # of decimal digits before decimal point. dscale is the
+	 * i is set to the # of decimal digits before decimal point. dscale is the
 	 * # of decimal digits we will print after decimal point. We may generate
 	 * as many as DEC_DIGITS-1 excess digits at the end, and in addition we
 	 * need room for sign, decimal point, null terminator.

src/include/tsearch/dicts/regis.h

@@ -2,7 +2,7 @@
  *
  * regis.h
  *
- * Declarations for for fast regex subset, used by ISpell
+ * Declarations for fast regex subset, used by ISpell
  *
  * Portions Copyright (c) 1996-2012, PostgreSQL Global Development Group
  *