[piexwasm] Makefile: remove unused -I compiler flag

There are no #include <files> present in the build (piex) directory so
the "-I ." flag does nothing anymore, remove it.

Bug: 935285
Change-Id: I7aa2c4c30f417c8a9930edf1f9e57badadcb71c2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1627836Reviewed-by: Alex Danilo <adanilo@chromium.org>
Commit-Queue: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#662976}

ui/file_manager/image_loader/piex/Makefile

@@ -16,7 +16,7 @@ PSRC = $(PIEX)/src/piex.cc \
        $(PIEX)/src/binary_parse/range_checked_byte_ptr.cc \
        $(PIEX)/src/binary_parse/cached_paged_byte_array.cc
 
-INCS = -I $(PIEX) -I .
+INCS = -I $(PIEX)
 WASM = -s WASM=1 -fno-exceptions -Wall -fsanitize=cfi -flto -fvisibility=hidden
 WOPT = -Os --llvm-opts 3 \
   -s STRICT=1 \