Fix inconsistencies in the code

This addresses a couple of issues in the code:
- Typos and inconsistencies in comments and function declarations.
- Removal of unreferenced function declarations.
- Removal of unnecessary compile flags.
- A cleanup error in regressplans.sh.

Author: Alexander Lakhin
Discussion: https://postgr.es/m/0c991fdf-2670-1997-c027-772a420c4604@gmail.com

src/include/executor/executor.h

@@ -314,7 +314,7 @@ ExecEvalExprSwitchContext(ExprState *state,
  * ExecProject
  *
  * Projects a tuple based on projection info and stores it in the slot passed
- * to ExecBuildProjectInfo().
+ * to ExecBuildProjectionInfo().
  *
  * Note: the result is always a virtual tuple; therefore it may reference
  * the contents of the exprContext's scan tuples and/or temporary results

src/include/executor/tablefunc.h

@@ -20,11 +20,11 @@ struct TableFuncScanState;
  * TableFuncRoutine holds function pointers used for generating content of
  * table-producer functions, such as XMLTABLE.
  *
- * InitBuilder initialize table builder private objects.  The output tuple
+ * InitOpaque initializes table builder private objects.  The output tuple
  * descriptor, input functions for the columns, and typioparams are passed
  * from executor state.
  *
- * SetDoc is called to define the input document.  The table builder may
+ * SetDocument is called to define the input document.  The table builder may
  * apply additional transformations not exposed outside the table builder
  * context.
  *
@@ -45,7 +45,7 @@ struct TableFuncScanState;
  * builder context such that each subsequent GetValue call returns the values
  * for the indicated column for the row being processed.
  *
- * DestroyBuilder shall release all resources associated with a table builder
+ * DestroyOpaque shall release all resources associated with a table builder
  * context.  It may be called either because all rows have been consumed, or
  * because an error occurred while processing the table expression.
  */