drop overridden definitions, drop useless mappings, and move a Rupee to an include

The first patch removes four pointless definitions of the Right Alt key in four Indian layouts -- they get overridden immediately afterwards.

The second patch removes useless modifier mappings that simply make the default ones again.

The third patch adds a Rupee sign by way of an include instead of a direct definition, because that is slightly clearer and matches the way that other layouts do it.