Make highmem classification of metalava optional

We have added a lot of metalava invocations since the highmem
differentation was added, most of which do not use a lot of memory.

By collecting data of max rss per process we have narrowed down
the set of highmem modules to a smaller set, and will annotate the
relevant modules as such.

Bug: 170701554
Test: NINJA_HIGHMEM_NUM_JOBS=3 m checkapi (no long tail of metalava)
Change-Id: Ic9c8c91388b02889111ef596fc6fd8bde9b42b9d