[Fuchsia] Remove fuchsia_target_api_level from .gn

We get this automatically from the //build checkout now

Bug: chromium:1432399
Change-Id: I99a307b496ab13c2d60ce76efa570709dabff1a2
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/112010
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Auto-Submit: Chong Gu <chonggu@google.com>
diff --git a/.gn b/.gn
index e39d6f7..b2bf99d 100644
--- a/.gn
+++ b/.gn
@@ -11,9 +11,6 @@
 script_executable = "python3"
 
 default_args = {
-  # Required for the Fuchsia SDK
-  fuchsia_target_api_level = 11
-
   # PDFs only need to run JavaScript.
   v8_enable_webassembly = false