• Fixes leading 'u' required on for json module  #8314 and then some

There were some accidental reversions to u-prefixes due to MP_REGISTER_MODULE() changes. But some tests still depended on u prefixes. I took the leap of removing all the u prefixes, getting most of the way toward micropython#9069, which does the same thing in MicroPython.

• Removed conditional import ufoo as foo stuff in the tests. This happens in top: Replace umodule with module everywhere. micropython/micropython#9069.
• Removed timeq/utimeq, which was not used anyway. It is also removed in top: Replace umodule with module everywhere. micropython/micropython#9069.
• Removed tests for things we are not supporting, such as MicroPython's btree, framebuf and usocket.
• Touched up extra_coverage auto-complete tests.
• Fixed a test or two that was mistakenly being skipped.