This fixes some possible heap buffer overflows, such as the following
triggered by our cmmi10.ttf:
```
ERROR: AddressSanitizer: heap-buffer-overflow on address 0x617000235709 at pc 0x7f95efd3c48a bp 0x7ffe41b6ecc0 sp 0x7ffe41b6ecb0
READ of size 1 at 0x617000235709 thread T0
#0 0x7f95efd3c489 in utf16be_to_ascii extern/ttconv/pprdrv_tt.cpp:178
#1 0x7f95efd3c489 in Read_name(TTFONT*) extern/ttconv/pprdrv_tt.cpp:339
#2 0x7f95efd499ef in read_font(...) extern/ttconv/pprdrv_tt.cpp:1325
#3 0x7f95efd4c602 in get_pdf_charprocs(...) extern/ttconv/pprdrv_tt.cpp:1420
#4 0x7f95efd35c22 in py_get_pdf_charprocs src/_ttconv.cpp:217
0x617000235709 is located 1 bytes to the right of 648-byte region [0x617000235480,0x617000235708)
allocated by thread T0 here:
#0 0x7f9612262a38 in __interceptor_calloc (/usr/lib64/libasan.so.4+0xdea38)
#1 0x7f95efd3b261 in GetTable(TTFONT*, char const*) extern/ttconv/pprdrv_tt.cpp:140
```
This makes all the tests pass for me, and removes an unused parameter.