Remove obsolete patch

lammps/COLVARS.cmake.diff

@@ -1,17 +0,0 @@
-diff --git a/cmake/Modules/Packages/COLVARS.cmake b/cmake/Modules/Packages/COLVARS.cmake
-index 745c1de026..b943a0345e 100644
---- a/cmake/Modules/Packages/COLVARS.cmake
-+++ b/cmake/Modules/Packages/COLVARS.cmake
-@@ -24,6 +24,12 @@ target_include_directories(colvars PUBLIC ${LAMMPS_LIB_SOURCE_DIR}/colvars)
- target_include_directories(colvars PRIVATE ${LAMMPS_SOURCE_DIR})
- target_link_libraries(lammps PRIVATE colvars)
-
-+if(BUILD_OMP)
-+  # Enable OpenMP for Colvars as well
-+  target_compile_options(colvars PRIVATE ${OpenMP_CXX_FLAGS})
-+  target_link_libraries(colvars PRIVATE OpenMP::OpenMP_CXX)
-+endif()
-+
- if(COLVARS_DEBUG)
-   # Need to export the define publicly to be valid in interface code
-   target_compile_definitions(colvars PUBLIC -DCOLVARS_DEBUG)