Revert "[Driver] Default riscv*- triples to -fdebug-default-version=4" (#84119)

This reverts commit bbc0f99f
(https://reviews.llvm.org/D157663).

With this change, `-g` for the next major release 19.1 will generate
R_RISCV_SET_ULEB128/R_RISCV_SUB_ULEB128 relocations, which require
lld>=18 or binutils>=2.41.
binutils 2.41 is relatively new, but GCC has been producing
R_RISCV_SET_ULEB128/R_RISCV_SUB_ULEB128 for some time now.