glsl2: Remove generate_temporary and global temporary counter.

Most places in the code simply use a static name, which works because
names are never used to look up an ir_variable.  generate_temporary is
simply unnecessary (and looks like it would leak memory, and isn't
thread safe...)

src/mesa/shader/ir_to_mesa.cpp

@@ -1938,7 +1938,6 @@ _mesa_glsl_compile_shader(GLcontext *ctx, struct gl_shader *shader)
    state->symbols = new(shader) glsl_symbol_table;
    state->info_log = talloc_strdup(shader, "");
    state->error = false;
-   state->temp_index = 0;
    state->loop_or_switch_nesting = NULL;
    state->ARB_texture_rectangle_enable = true;