Remove platform alt headers for testing

All the platform configuration is in the crypto submodule, so the headers to
test it should be there.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

Author: gilles-peskine-arm

doxygen/mbedtls.doxyfile

@@ -6,7 +6,7 @@ EXTRACT_ALL            = YES
 EXTRACT_PRIVATE        = YES
 EXTRACT_STATIC         = YES
 CASE_SENSE_NAMES       = NO
-INPUT                  = ../include input ../tf-psa-crypto/include ../tests/include/alt-dummy
+INPUT                  = ../include input ../tf-psa-crypto/include
 FILE_PATTERNS          = *.h
 EXCLUDE                = ../tf-psa-crypto/include/mbedtls/private
 RECURSIVE              = YES