Remove BLanguage section whose content can be found on the wiki

src/docs/chapter/user/12_BLanguage/00_section_header.adoc

...ocs/chapter/user/12_BLanguage/01_Current_Limitations.adoc

...ocs/chapter/user/12_BLanguage/01_Summary_of_B_Syntax.adoc

src/docs/chapter/user/12_BLanguage/02_Types.adoc

src/docs/chapter/user/12_BLanguage/03_Deferred_Sets.adoc

...docs/chapter/user/12_BLanguage/10_External_Functions.adoc

...r/user/12_BLanguage/11_Recursively_Defined_Functions.adoc

src/docs/chapter/user/12_BLanguage/13_Memoization.adoc

src/docs/chapter/user/12_BLanguage/20_Tips_B_Idioms.adoc

...er/user/12_BLanguage/21_Tips_Writing_Models_for_ProB.adoc

src/docs/chapter/user/12_BLanguage/22_Debugging.adoc

...er/12_BLanguage/Tutorial_Modeling_Infinite_Datatypes.adoc

src/docs/chapter/user/12_BLanguage/WD/00_section_header.adoc

...er/user/12_BLanguage/WD/01_Well-Definedness_Checking.adoc

src/docs/chapter/user/12_BLanguage/WD/ZZ_section_footer.adoc

src/docs/chapter/user/12_BLanguage/ZZ_section_footer.adoc