Reduce thread count for 719-varhandle-concurrency test

This includes the revert of the temporary measure for the failing
test (Ie4f11f53b8b3fb1507bf7dc0a2dae018f48aa573).

Fixes: 229958698
Test: Reverted arm32 register clobbering fix and see test still
      catches the error
      (see I14d51f0aa1e26de82be7077ac5597bbeec476dcd)
Change-Id: I49a399826cc09863f2ea3ebdf40acf5845892f7f
2 files changed