Remove unused modexp512-x86_64.pl.

See upstream's c436e05bdc.

Change-Id: I7cbe5315a769450e4630dd4e8f465cdfd45c2e08
Reviewed-on: https://boringssl-review.googlesource.com/3025
Reviewed-by: Adam Langley <agl@google.com>

crypto/bn/CMakeLists.txt

@@ -7,7 +7,6 @@ if (${ARCH} STREQUAL "x86_64")
 		asm/x86_64-gcc.c
 		x86_64-mont.${ASM_EXT}
 		x86_64-mont5.${ASM_EXT}
-		modexp512-x86_64.${ASM_EXT}
 		rsaz-x86_64.${ASM_EXT}
 		rsaz-avx2.${ASM_EXT}
 
@@ -61,7 +60,6 @@ add_library(
 
 perlasm(x86_64-mont.${ASM_EXT} asm/x86_64-mont.pl)
 perlasm(x86_64-mont5.${ASM_EXT} asm/x86_64-mont5.pl)
-perlasm(modexp512-x86_64.${ASM_EXT} asm/modexp512-x86_64.pl)
 perlasm(rsaz-x86_64.${ASM_EXT} asm/rsaz-x86_64.pl)
 perlasm(rsaz-avx2.${ASM_EXT} asm/rsaz-avx2.pl)
 perlasm(bn-586.${ASM_EXT} asm/bn-586.pl)