Revert "[dwarfdump] Add missing DW_LANG_Mips_Assembler case to LanguageString()"

This reverts commit 93c7e6161e1adbd2c7ac81fa081823183035cb64.

This commit got approved first, but was dependant on another one going in (The one pretty printing attribute values). I'll reapply when the other one is in.

llvm-svn: 217183