glsl: Don't add structure fields to the symbol table

glsl: Don't add structure fields to the symbol table

I erroneously added this back in January 2011 in commit 88421589.
Looking at the commit message, I have no idea why I added it.  It only
added non-array structure fields to the symbol table, so array structure
fields are treated correctly.

Fixes piglit tests structure-and-field-have-same-name.vert and
structure-and-field-have-same-name-nested.vert.  It should also fix
WebGL conformance tests shader-with-non-reserved-words.

NOTE: This is a candidate for the stable release branches.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=57622
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
(cherry picked from commit ed3f237e09a42bdb55afb58d1536affad9000d76)