Delete some special-case logic for IE < 7, as well as some handling for IE 10 emulating IE 5.
Delete some special-case logic for IE < 7, as well as some handling for IE 10 emulating IE 5.

The IE < 7 logic is long unsupported, and the working assumption is that no code we need to support is depending on IE 5 emulation, either.

RELNOTES[INC]: Stop handling IE 5 emulation quirks.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=251519702

google/closure-library,lucidsoftware/closure-library,google/closure-library,lucidsoftware/closure-library,google/closure-library,lucidsoftware/closure-library,lucidsoftware/closure-library,google/closure-library,google/closure-library