Revert "glsl: fix xfb_offset unsized array validation"

This reverts commit aac90ba292.

The commit caused a regression in:
piglit.spec.glsl-1_50.compiler.gs-input-nonarray-named-block.geom

Also the CTS test it was meant to fix seems like it may be bogus.

Cc: "12.0" <mesa-stable@lists.freedesktop.org>

src/compiler/glsl/ir.h

@@ -2621,9 +2621,6 @@ is_gl_identifier(const char *s)
    return s && s[0] == 'g' && s[1] == 'l' && s[2] == '_';
 }
 
-const glsl_type *
-get_varying_type(const ir_variable *var, gl_shader_stage stage);
-
 extern "C" {
 #endif /* __cplusplus */