Revert "Disable PRODUCT_ART_USE_READ_BARRIER for MIPS devices"

Not needed anymore since we just merged read barrier support
for MIPS: https://android-review.googlesource.com/#/c/353332/.

Test: "testrunner.py --target --optimizing --32 -j2" on CI20
Test: "make -j2 test-art-target-gtest32" on CI20

This reverts commit 5df6dba9ab7ceb11e6a20e760ded6374a410fed9.

Change-Id: Idfc0dd19b7394f4792599a0cc5a6193d590f1b7c
3 files changed
tree: 25f41ee3169d699d3df9f0c8a456b3ee4fac0ad6
  1. arm_krait/
  2. armv8/
  3. mips32r2_fp/
  4. mips32r2_fp_xburst/
  5. mips64r6/
  6. silvermont/