glsl: remove unneeded check for incompatible primitive types in GS

glsl: remove unneeded check for incompatible primitive types in GS

The validation of the default in layout qualifier already assures that
we won't have 2 ast_gs_input_layout objects with different primitive
type values. In fact, the validation already assures that we won't
have 2 ast_gs_input_layout objects in the AST tree at all.

The check for an error in the shader has been replaced by an assert.

Reviewed-by: Timothy Arceri <timothy.arceri@collabora.com>
Signed-off-by: Andres Gomez <agomez@igalia.com>