glsl: Remove unused include from glsl_symbol_table.h

glsl: Remove unused include from glsl_symbol_table.h

Only function-defs use glsl_type so forward declare instead.
Compile-tested on my Ivy-bridge system.

IWYU also suggests removing #include <new>, and this compiles fine.
I'm not familiar enough with memory management in C/C++ that I feel
comfortable removing this. Insights would be appreciated.

Reviewed-by: Tom Stellard <thomas.stellard@amd.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Signed-off-by: Thomas Helland <thomashelland90@gmail.com>