[MINOR][CORE] Cleanup dead code and duplication in Mem. Management

## What changes were proposed in this pull request?

* Removed the method `org.apache.spark.sql.catalyst.expressions.codegen.UnsafeRowWriter#alignToWords`.
It became unused as a result of 85b0a157
(SPARK-15962) introducing word alignment for unsafe arrays.
* Cleaned up duplicate code in memory management and unsafe sorters
  * The change extracting the exception paths is more than just cosmetics since it def. reduces the size the affected methods compile to

## How was this patch tested?

* Build still passes after removing the method, grepping the codebase for `alignToWords` shows no reference to it anywhere either.
* Dried up code is covered by existing tests.

Author: Armin <me@obrown.io>

Closes #19254 from original-brownbear/cleanup-mem-consumer.