solvers: Fix incorrect f_OPHOL declaration

[Tatsh]

gentoo/gentoo#39303
coin-or-tools/ThirdParty-ASL#8

This change fixes the following issue with LTO:

solvers/fgh_read.c:101:15: error: function 'f2_HOL_ASL' redeclared as variable
  101 |  extern char* f_OPHOL;
      |               ^
solvers/rops2.c:1019:1: note: previously declared here
 1019 | f_OPHOL(expr *e A_ASL)
      | ^
lto1: fatal error: errors during merging of translation units
compilation terminated.

[Tatsh]

File was removed. Closing.