meson: Remove usage of use_elf_tls

After c47fd3dc00 ("windows: Use TLS context/dispatch with shared-glapi")

use_elf_tls are always setting to true, so we can remove it safety

Signed-off-by: Yonggang Luo <luoyonggang@gmail.com>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17213>

meson.build

@@ -504,7 +504,6 @@ foreach platform : _platforms
   pre_args += '-DHAVE_@0@_PLATFORM'.format(platform.to_upper())
 endforeach
 
-use_elf_tls = true
 pre_args += '-DUSE_ELF_TLS'
 
 if with_platform_android and get_option('platform-sdk-version') >= 29

src/meson.build

@@ -152,7 +152,7 @@ if with_glx != 'disabled' and not with_glvnd
     libraries : libgl,
     libraries_private : gl_priv_libs,
     requires_private : gl_priv_reqs,
-    variables : ['glx_tls=@0@'.format(use_elf_tls ? 'yes' : 'no')],
+    variables : ['glx_tls=yes'],
   )
 endif