Update the spec test suite submodule

[alexcrichton]

Delete the local copies of the relaxed-simd test suite as well as they're now incorporated.

Closes #5914

[alexcrichton]

The test failures here I think are due to OOM for QEMU taking too much memory. After some investigation I found out that some of the new multi-memory tests add a few (memory 0 0) to modules to test when the memory index isn't 0 (and the "main memory" is somewhere in the middle of the index space. These 0-sized 0-max-size memories, however, were getting compiled as static memories (the "maximum size" is 0 after all) which meant they got static memory guards which was 4G of virtual memory which is a known way to get QEMU to OOM.

I've updated the test suite so that when under QEMU emulation we not only force dynamic memories but additionally all guards are removed. This further drastically reduces the virtual memory footprint, as intended, when under emulation and I think should make this landable.

FWIW running the spec tests in QEMU on my local machine took 1.3G max RSS prior and now it takes 250M so hopefully a nice improvement!